Charles Lyell

(1797-1875)

Lyell, Sir Charles.  (1873).  Geological Evidences of The Antiquity of Man.  (4^th ed.).  New York:  AMS Press.

Background Information on Charles Lyell

Charles Lyell was born November 14 1797 at Kinnordy, a family estate near Forfar, of England (Bailey 1).  His studies began at a school in Ringwood until father Charles Lyell decided to move him to Salisbury to learn under Dr. Radcliffe, an Oxonian classical scholar (Bailey 6).  Lyell’s first involvement of natural history took place while recovering from an illness by means of collecting insects, identifying them with pictures of his father’s books, and watching their transformations (Bailey 8).  He later attended school in Midhurst and then college in Oxford (Bailey 14).  After Oxford, Lyell joined William Henry Fitton to become Secretaries of the Geological Society (Bailey 53) and later visited Paris to conduct research and improve his international language of sciences making him well known (Wilson 3).  Since the public at that time had great interest in all sciences, Lyell thought it would be wise to put his conception of geology on paper and attempt to use it as a source of income (Wilson 3).  His ideas of geology were described in such length it led him to write a book on the “principles” of science, which became Principles (Wilson 4).  He later wrote Principles of Geology, Elements of Geology, Manual of Geology, and Antiquity of Man (Wilson 33). 

Part III

The Origin of Species as Bearing Upon Man’s Place in Nature

Chapter XX

Theories of Progression and Transmutation

…Before I attempt to explain a great step, which has recently been made by Mr. Darwin and his fellow-laborers in this field of enquiry, I think it is useful to recapitulate here some of the leading features of Lamarck’s system, without attempting to adjust the claims of some of his contemporaries (Geoffroy St. Hilaire in particular) to share in the credit of some of his original speculations.

            From the time of Linnaeus to the commencement of the present century, it seemed a sufficient definition of the term species to say, that ‘a species consisted of individuals all resembling each other, and reproducing their like by generation.’  But Lamarck, after having first studied botany with success, had then turned his attention to conchology, and soon became aware that in the newer (or tertiary) strata of the earth’s crust there were a multitude of fossil species of shells, [435] some of them identical with the living ones, others simply varieties of the living, and which, as such were entitled to be designated, according to the ordinary rules of classification, by the same names.  He also observed that other shells were so nearly allied to living forms, that it was difficult not to suspect that they had been connected by a common bond of descent.  He therefore proposed that the element of time should enter into the definition of a species, and that it should run this:  ‘A species consists of individuals all resembling each other, and reproducing their like by generation, so long as the surrounding conditions do not undergo changes sufficient to cause their habits, characters, and forms to vary.’  He came at last to the conclusion, that none of the animals and plants now existing were primordial creations, but were all derived from pre-existing forms, which, after they may have gone on for indefinite ages reproducing their like, had, at length, by the influence of alterations in climate and in the animate world, been made to vary gradually, and adapt themselves to new circumstances, some of them deviating, in the course of ages, so far from their original type as to have claims to be regarded as new species.

            In support of these views, he referred to wild and cultivated plants, and to wild and domesticated animals, pointing out how their colour, form, structure, physiological attributes, and even insects, were gradually modified by exposure to new soils and climates, new enemies, modes of subsistence, and kinds of food.

            Nor did he omit to notice that the newly acquired peculiarities may be inherited by the offspring for an indefinite series of generations, whether they be brought about naturally,--as when a species, on the extreme verge of its geographical range, comes into competition with new antagonists, and is subjected to new physical conditions; or artificially,--as when, by the [436] act of the breeder or horticulturist, peculiar varieties of form or disposition are selected.

            But Lamarck taught not only that species had been constantly undergoing changes from one geological period to another, but that there also had been a progressive advance of the organic world from the earliest to the latest times, from beings of the simplest to those of more and more complex structure, and from the lowest instincts up to the highest, and, finally, from brute intelligence to the reasoning powers of Man.  The improvement in the grade of being had been slow and continuous, and the human race itself was at length evolved out of the most highly organised and endowed of the inferior mammalia.

            In order to explain how, after an indefinite lapse of ages, so many of the lowest grades, of animal or plant, still abounded, he imagined that the germs or rudiments of living things, which he called monads, were continually coming into the world, and that there were different kinds of these monads for each primary division of the animal and vegetable kingdoms.  This last hypothesis does not seem essentially different from the old doctrine of equivocal or spontaneous generation; which, after all the able and conscientious experiments of Mr. Bastian, is still as much a matter of controversy as it was in the days of Lamarck.

            Some of the laws which govern the appearance of new varieties were clearly pointed out by Lamarck.  He remarked, for example, that as the muscles of the arm become strengthened by exercise or enfeebled by disuse, some organs may in this way, in the course of time, become entirely obsolete, and others previously weak become strong and play a new or more leading part in the organisation of a species.  And so with instincts, where animals experience new [437] dangers they become more cautious and cunning, and transmit these acquired faculties to their posterity.  But not satisfied with such legitimate speculations, the French philosopher conceived that by repeated acts of volition animals might acquire new organs and attributes, and that in plants, which could not exert a will of their own, certain subtle fluids or organising forces might operate so as to work out analogous effects.

            After commenting on these purely imaginary causes, I pointed out in 1832, s the two great flaws in Lamarck’s attempt to explain the origin of species, first, that he had failed to adduce a single instance of the initiation of a new organ in any species of animal or plant; and secondly, that variation, whether taking place in the course of nature or assisted artificially by the breeder and horticulturist, had never yet gone so far as to produce two races sufficiently remote from each other in physiological constitution as to be sterile when intermarried, or, if fertile, only capable of producing sterile hybrids &c.

            To this objection Lamarck would, no doubt, have answered that there had not been time for bringing out a out so great an amount of variation; for when Cuvier and some other of his contemporaries appealed to the embalmed animals and plants taken from Egyptian tombs, some of them 3,000 years old, which had not experienced in that long period the slightest modification in their specific characters, he replied that the climate and soil of the valley of the Nile had not varied in the interval, and that there was therefore no reason for expecting that we should be able to detect any change in the fauna and flora.  ‘But if,’ he went on to say, ‘the physical geography, temperature, and other conditions of life, had been altered in Egypt as much as we know from geology has happened in [438] other regions, some of the same animals and plants would have deviated so far from their pristine types as to be thought entitled to take rank as new and distinct species.’

            Although I cited this answer of Lamarck, in my account of his theory, I did not, at the time, fully appreciate the deep conviction which it displays of the slow manner in which geological changes have taken place, and the insignificance of thirty or forty centuries in the history of a species, and that, too, at a period when vary narrow views were entertained of the extent of past time by most of the ablest geologists, and when great revolutions of the earth’s crust, and its inhabitants, were generally attributed to sudden and violent catastrophes.

            While, in 1832, I argued against Lamarck’s doctrine of the gradual transmutation of one species into anther, I agreed with him in believing that the system of changes now in the progress in the organic world would afford, when fully understood, a complete key to the interpretation of all the vicissitudes of the living creation in past ages.  I contended against the doctrine, then very popular, of the sudden destruction of vast multitudes of species, and the abrupt ushering into the world of new batches of plants and animals [439].

Part III

The Origin of Species as Bearing Upon Man’s Place in Nature

Chapter XXI

On the Origin of Species by Variation and Natural Selection

            For many years after the promulgation of Lamarck’s doctrine of progressive development, geologists were much occupied with the question whether the past changes in the animate and inanimate world were brought about by sudden and paroxysmal action, or gradually and continuously, by causes differing neither in kind nor degree from those now in operation.

            An anonymous author published in 1844 ‘The Vestiges of Creation,’ a treatise, written in a clear and attractive style, which made the English public familiar with the leading views of Lamarck on transmutation and progression, but brought no new facts or original line of argument to [454] support those views, or to combat the principal objections which the scientific world entertained against them.

            No decided step in this direction was made until the publication in 1858 of two papers, one by Mr. Darwin and another by Mr. Wallace, followed in 1859 by Mr. Darwin’s celebrated work on ‘The Origin of Species by Means of Natural Selection; or, the Preservation of favoured Races in the Struggle for Life.’  The author of this treatise had for twenty previous years strongly inclined to believe that variation and the ordinary laws of reproduction were among the secondary causes always employed by the Author of Nature, in the introduction from time to time of new species into the world, and he had devoted himself patiently to the collecting of facts, and making of experiments in zoology and botany, with a view of testing the soundness of the theory of transmutation [455].

...The trial of strength, which must decide what individuals are to survive and what to succumb, occurs in the season when the means of subsistence are fewest, or enemies most numerous, or when the individuals are enfeebled by climate or other causes; and it is then that those varieties which have any, even the slightest, advantage over others come off victorious.  They may often owe their safety to what would seem to a causal observer a trifling difference, such as a darker or lighter shade of colour rendering hem less visible to a species which preys upon them, or sometimes to attributes more obviously advantageous, such as greater cunning, or superior powers of flight or swiftness of foot.  These peculiar qualities and faculties, bodily and instinctive, may enable them to outlive their less favoured rivals, and being trans- [456] mitted by the force of inheritance to their offspring, will constitute new races, or what Mr. Darwin calls ‘incipient species.’  If one variety, being in other respects just equal to its competitors, happens to be more prolific, some of its offspring will stand a greater chance of being among those which will escape destruction, and their descendants, being in like manner very fertile, will continue to multiply at the expense of all less prolific varieties.

            As breeders of domestic animals, when they choose certain varieties in preference to others to breed from, speak technically of their method as that of ‘selecting,’ Mr. Darwin calls the combination of natural causes, which may enable certain varieties of wild animals or plants to prevail over others of the same species, ‘natural selection.’

            A breeder finds that a new race of cattle with short horns or without horns may be formed, in the course of several generations, by choosing varieties having the most stunted horns as his stock from which to breed; so nature, by altering, in the course of ages, the conditions of life, the geographical features of a country, its climate, the associated plants and animals, and, consequently, the food and enemies of a species and its mode of life, may be said, by this means, to select certain varieties best adapted for the new state of things.  Such new races may often supplant the original type from which they have diverged, although that type may have been perpetuated without modification for countless anterior ages in the same region, so long as it was in harmony with the surrounding conditions then prevailing.

            Lamarck, when speculating on the origin of the long neck of the giraffe, imagined that quadruped to have stretched himself up in order to reach the boughs of lofty trees, until by continued efforts, and longing to reach higher, he obtained an elongated neck.  Mr. Darwin and Mr. Wallace simply suppose that, in a season of scarcity, the longer-neck indi- [457] viduals, having the advantage in this respect over the rest of the herd, as being able to browse on foliage out of their reach, survived them, and transmitted their peculiarity of cervical conformation to their successors.

            By the multiplying of slight modifications in the course of thousands of generations, and by the handing down of the newly-acquired peculiarities by inheritance, a greater and greater divergence from the original standard is supposed to be effected, until what may be called a new species, or, in a greater lapse of time, a new genus, will be the result.

            Every naturalist admits that there is a general tendency in animals and plants to vary; but it is usually taken for granted, though we have no means of proving the assumption to be true, that there are certain limits beyond which each species cannot pass under any circumstances, or in any number of generations.  Mr. Darwin and Mr. Wallace say that the opposite hypothesis, which assumes that every species is capable of varying indefinitely from its original type, is not a whit more arbitrary, and has this manifest claim to be preferred, that it will account for a multitude of phenomena which the ordinary theory is incapable of explaining.

            We have no right, they say, to assume, should we find that a variable species can no longer be made to vary in a certain direction, that it has reached the utmost limit to which it might, under more favourable conditions, or if more time were allowed, be made to diverge from the parent type, and this view is supported by the fact, that our oldest domestic animals and cultivated plants, those which have varied most widely from the original parent stock, still continue to produce new varieties and show no sign whatever of ceasing to vary.

            Hybridisaton is not considered by Mr. Darwin as a cause of new species, but rather as tending to keep variation within bounds.  Varieties which are nearly allied cross readily [458] with each other, and with the parent stock, and such crossing tends to keep the species true to its type, while forms which are less nearly related, although they may intermarry, produce no mule offspring capable of perpetuating their kind [459].

...The theory of indefinite modification would also explain why rudimentary organs are so useful in classification, being the remnants preserved by inheritance of organs which the [460] ancestors of the presents species once used—as in the case of the rudiments of eyes in insects and reptiles inhabiting dark caverns, or of the wings of birds and beetles which have lost all power of flight.  In such cases the affinities of species are often more readily discerned by reference to these imperfect structures than by others of much more physiological importance to the individuals themselves.

            The same hypothesis would explain why there are no mammalia in islands far from continents, except bats, which can reach them by flying; and also why the birds, insects, plants, and other inhabitants of islands, even then specifically unlike, usually agree generically with those of the nearest continent, it being assumed that the original stock of such species came by migration from the nearest land.

            Variation and natural selection would also afford a key to a multitude of geological facts otherwise wholly unaccounted for, as, for example, why there is generally an intimate connection between the living animals and plants of each great division of the globe and the extinct fauna and flora of the post-tertiary or tertiary formations of the same region; as, for example, in North America, where we not only find among the living mollusca peculiar forms foreign to Europe, such as Gnathodon and Fulgar (a subgenus of Fusus), but meet also with extinct species of those same genera in the tertiary fauna of the same part of the world.  In like manner, among the mammalia we find in Australia not only living kangaroos and wombats, but fossil individuals of extinct species of the same genera.  So also there are recent and fossil sloths, armadilloes, and other edentata in South America, and living and extinct species of elephant, rhinoceros, tiger, and bear in the great Europeo-Asiatic continent.  The theory of the origin of new species by variation will also explain why a species which has once died out never reappears, and why the fossil fauna and flora recede farther and farther from the living type in propor- [461] tion as we trace it back to remoter ages.  It would also account for the fact, that when we have to intercalate a new set of fossiliferous strata between two groups previously known, the newly-discovered fossils serve to fill up gaps between specific and generic types previously familiar to us, supplying often the missing links of the chain, which if transmutation is accepted, must once have been continuous.

            One of the most original speculations in Mr. Darwin’s work is derived from the fact that, in the breeding of animals, it is often observed that at whatever age any variation appears in the parent, it tends to reappear at a corresponding age in the offspring.  Hence the young individuals of two races which have sprung from the same parent stock are usually more like each other than the adults.  Thus the puppies of the greyhound and bull-dog are much more nearly alike in their proportions than the grown-up dogs, and in like manner the foals of the cart and racehorse than the adult individuals.  For the same reason we may understand why the species of the same genus, or genera of the same family, resemble each other more nearly in the embryonic than in their more fully developed state, or how it is that in the eyes of most naturalist the structure of the embryo is even more important in classification than that of the adult, ‘for the embryo is the animal in its less modified state, and in so far it reveals the structure of its progenitor.  In two groups of animals, however much they may at present differ from each other in structure and habits, if they pass through the same or similar embryonic stages, we may feel assured that they have both descended from the same or nearly similar parents, and are therefore in that degree closely related.  Thus community in embryonic structure reveals community of descent, however much the structure of the adult may have been modified.’ [462].

            If then there had been a system of progressive development, the successive changes through which the embryo of a species of a high class, a mamifer, for example, now passes, may be expected to present us with a picture of the stages through which, in the course of ages, that class of animals has successively passed in advancing from a lower to a higher grade.  Hence the embryonic states exhibited one after the other by the human individual bear a certain amount of resemblance to those of the fish, reptile, and bird before assuming those of the highest division of the vertebrata.

            Mr. Darwin, after making a laborious analysis of many floras, found that those genera which are represented by a large number of species contain a grater number of variable species, relatively specking, than the smaller genera, or those less numerously represented.  This fact he adduces in support of his opinion that varieties are incipient species, for he observes that the existence of the larger genera implies, in the period immediately preceding our own, that the manufacturing of species has been active, in which case we ought generally to find the same forces still in full activity, more especially as we have every reason to believe the process by which new species are produced is a slow one [463].

Synopsis

            Charles Lyell was an English geologist who contributed greatly in the field of natural history and has made a lasting effect on the idea of evolution.  Lyell opposed the idea of catastrophism (the belief that catastrophes caused a lot of change to the earth in a short amount of time) and claimed that the earth had been formed by the same kinds of processes that we see today (MacLachlan 205).  He “whole-heartedly” followed Scottish geologist James Hutton in support for his Uniformitarian doctrine that assumed that the earth is run on perfect principles, which being perfect, know no change (Bailey 85).  With these beliefs, Lyell described his conception of geology in several books.  In particular, his book, Geological Evidences of The Antiquity of Man, is the more recent and revised book that takes a look at his ideas of evolution in accordance with Charles Darwin and Jean Baptiste de Lamarck. 

            Charles Lyell and Charles Darwin agreed that catastrophic explanation was advocating supernatural interference with natural laws (Recker 467).  However they had conflicted views on the idea of transmutation.  Lyell used the imperfection of the fossil record to argue against “progressive development” and hence transmutation, while Darwin used it to explain away the lack of transitional forms, and hence to support transmutation (Recker 467).  In response to Darwin’s theory Lyell later reprinted in Principles a critical analysis of Lamarck’s theory of transmutation in which he upheld the fixity of species, although he had also shown ‘that the gradual extinction of species was part of the constant and regular course of nature’ (Wilson 34). 

            In Geological Evidences of The Antiquity of Man [454] Lyell discusses the anonymous Vestiges of the Natural History of Creation and describes the events leading up to Alfred Russel Wallace and Darwin’s theory of natural selection (Wilson 34).  Lyell says that in the Origin of Species Darwin shows not only how new races and species might arise by natural selection, but also how this theory explained many different and previously unconnected biological phenomena (Wilson 34).  Lyell later said that the theory of variation and natural selection would explain such relationships (of dispersed plants and animals), but no other hypothesis for the origin of species would do so (Wilson 35).  Although Lyell originally felt partial to such an idea, based on his belief in uniformitarianism stating that existing causes could not produce all the known geological phenomena, eventually he accepted Darwin’s theory of natural selection with one fundamental reservation—“The theory would account for the selection of variations favourable to a species in the struggle for existence, but it could not account for the origin of the variations to be selected” (Recker 470 & Wilson 35). 

            After Lyell’s acceptance of Darwin’s natural selection, soon came the acceptance of the idea of animal descent from man.  This theory of transmutation could explain the unity of morphological type throughout the whole organic world (Cohen 87).  Darwin’s theory of “common descent through phylogeny’ presented a simpler, more materialistic clarification, explaining not only the ‘existence of ‘rudimentary organs’, but also many biogeographical features (Cohen 87).  Lyell supports this in his Geological Evidences of The Antiquity of Man [461] when he explains why there are no mammals in islands far from continents, except bats, which can reach them by flying (Cohen 88).  Lyell’s acceptance of Darwin’s “transmutation of species” entered his thinking on geochronology since “he specified that his computation did not violate its intent, and he employed the Darwinian explanation for speciation:  very small changes over very long spans of time to arrive at the probable duration of the geological periods” (Tasch 442).  Lyell’s view of the theories of Darwin “consist largely in a commitment concerning the direction that natural history should take, and a recognition that Darwin’s explanatory scheme was the most promising candidate for acheieving this goal” (Recker 473).  Still, after accepting Darwin’s idea of natural selection, Lyell a bit wary attempted to preserve something of a “spiritualist view” of human evolution (Cohen 88).

            As for the “creation” of new species, the idea remained an unsolved puzzle to Lyell.  While he outlined an evolutionary history of human species, he could not present any evidence of its origin, but nonetheless suggested that evolutionary theory might ultimately be applicable to human beings (Hallam 136).  The main issue was the status of mind and consciousness, and he refers to ‘new and powerful causes to explain the spiritual part of human nature’; he could not accept humanity’s place ‘among the brutes’ (Hallman 136).

            He and Leopold Cuvier were capable of sharing a belief that lead to species extinction; the belief that a continually changing physical environment would lead to shifting patterns of ecological conditions (Hallam 134).  This shifting of patterns of ecological conditions is addressed in Lyell’s Geological Evidences of The Antiquity of Man [438] when discussing the physical geography, climate, and conditions of life.  In addition, Lyell explained that a species could become extinct by competing for food with a better endowed species—and losing, otherwise known as Lyell’s “struggle for existence” (MacLachlan 206).

            In an attempt to understand Charles Lyell’s views, one must consider how he came to believe what he did and why he chose to believe in that.  The belief in uniformitarianism came from his studying under Hutton.  Hutton greatly admired the work of Sir Isaac Newton and even based his writing style on him (Baker 173).  As Newton invented an ideal mechanical theory for the solar system in a heliocentric manner, Hutton envisioned a revolutionary and cyclic system of an Earth history (Baker 173).  Lyell recognized Hutton’s goal of constructing fixed principles in accordance to geology in the same manner that Newton did for astronomy (Baker 174).  Lyell not only had the goal of establishing a system for the Earth, but also the vision of a specific method where this could be accomplished (Baker 174).  To avoid the presumption of ordinary forces and the idea of time never being able to explain geological phenomena, Lyell avoided paroxysms and catastrophes and believed it was necessary to stipulate the true nature of those forces (Baker 174). 

            Lyell clearly thought the task of a geologist was to explain geological phenomena through principles or logical propositions of true causes or vera causae (Baker 175).  He even went about naming his first treatise after Newton’s Principia, which is based on then notion of logical principles governing the motion of bodies.  As a man in his thirties, Lyell stood out and his works signaled substantial scientific ambitions (Rudwick 4).

            In Lyell’s later years his one creation capable of standing alone and representing a sound scientific work would be his Geological Evidences of The Antiquity of Man.  In Part I the first chapter discusses the geological time significance of the Recent and Post-Pliocene terms.  Chapters two and three deal with recent times of fossils of human remains, Danish, Swiss, Irish, American, and Scottish finds.  Chapters four and five discuss the Pleistocene period collecting bones of man and extinct mammalian and human and Neanderthal skulls.  One particular quote Lyell says in describing the great difference between the two skulls is:

            The direct bearing of the ape-like character of the Neanderthal skull on Lamarck’s doctrine of progressive development and transmutation, or on that modification of it which has of late been so ably advocated by Mr. Darwin, consists in this, that the newly observed deviation from a normal standard of human structure is not in a casual or random direction, but just what might have been anticipated if the laws of variation were just such as the transmutationists require. (Bailey 199)

Chapters six discusses flint implements in cave-deposits, while chapters seven, eight, and nine continue to examine the Pleistocene period and evaluated other bones and flint implements of valleys and caves.  Chapters ten and eleven look at the French and English fossils and art pieces.

            In Part II of Geological Evidences of The Antiquity of Man chapters twelve through eighteen discuss the glacial period of Europe and North America.  Chapter nineteen summarizes the geological proofs of the previous chapters.  In Part III twenty mainly discusses the theories of transmutation in particular the views of Darwin and Lamarck that were earlier addressed.  Chapter twenty-one discusses perhaps the most debatable material in explaining the origin of species, while chapters twenty-two through twenty-four discuss the development and objection to developments of species and their languages, and what man’s purpose if for here on earth.

            Charles Lyell was a crucial scientist in developing the idea of evolution.  His questions, objections, and creative principles pushed other famous scientists of his time to examine and evaluate their beliefs.  Lyell was a scientist that held his own based on his belief structure, who strived to find an answer, yet was willing to make adjustments in his theories.  Future scientists can take heart in the fact that although Lyell did not produce any lasting theories of his own, his scientific attitude allowed him to make a contribution to science through his dialogues with Darwin, Cuvier, and others.  This type of contribution is essential for the development of new scientific advancements and discoveries.

References

Bailey, Edward.  Charles Lyell.  Garden City, New York:  Doubleday & Company, Inc., 1963.

Cohen, Claudine. "Charles Lyell and the evidences of the antiquity of man."  Lyell:  the Past is the Key to the Present.  Ed. Blundell, D.J. & Scott, A. C.  London:  The Geological Society, 1998. 83-93.

Hallam, A.  "Lyell's views on organic progression, evolution and extinction."  Lyell:  the Past is the Key to the Present.  Ed. Blundell, D.J. & Scott, A. C.  London:  The Geological Society, 1998. 133-136.

Lyell, Sir Charles.  The Geological Evidences of The Antiquity of Man.  (4^th ed.).  New York:  AMS Press 1873.

MacLachlan, James.  Children of Prometheus.  Toronto:  Wall & Emerson, Inc., 1988.

Recker, Doren.  "There's More than One Way to Recognize a Darwinian:  Lyell's Darwinism."  Philosophy of Science.  57.3 (1990):  459-478.

Rudwick, Martin.  "Lyell and the Principles of Geology."  Lyell:  the Past is the Key to the Present.  Ed. Blundell, D.J. & Scott, A. C.  London:  The Geological Society, 1998.  3-15.

Rudwick, Martin.  "The Strategy of Lyell's Principles of Geology."  Isis.  61.1 (1970):  4-33.

Silliman, Robert.  "The Hamlet Affair:  Charles Lyell and the North Americans."  Isis.  86.4 (1995):  541-561.

Tasch, Paul.  "Lyell's Geochronological Model:  Published Year Values for Geological Time."  Isis.  68.3 (1977):  440-442.

Wilson, L.G.  "Lyell:  the man and his times."  Lyell:  the Past is the Key to the Present.  Ed. Blundell, D.J. & Scott, A. C.  London:  The Geological Society, 1998.  21-37.

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