Lamarck, the Founder of Evolution: His Life and Work

by A. S. Packard

Such were the amount and kind of knowledge regarding the origin and structure of our earth which existed at the close of the eighteenth century, while Lamarck was meditating his Hydrogéologie, and had begun to study the invertebrate fossils of the Paris tertiary basin.

His object, he says in his work, is to present certain considerations which he believed to be new and of the first order, which had escaped the notice of physicists, and which seemed to him should serve as the foundations for a good theory of the earth. His theses are:

1. What are the natural consequences of the influence and the movements of the waters on the surface of the globe?

2. Why does the sea constantly occupy a basin within the limits which contain it, and there separate the dry parts of the surface of the globe always projecting above it?

3. Has the ocean basin always existed where we actually see it, and if we find proofs of the sojourn of the sea in places where it no longer remains, by what cause was it found there, and why is it no longer there?

4. What influence have living bodies exerted on the substances found on the surface of the earth and which compose the crust which invests it, and what are the general results of this influence?

Lamarck then disclaims any intentions of framing brilliant hypotheses based on supposititious principles, but nevertheless, as we shall see, he falls into this same error, and like others of his period makes some preposterous hypotheses, though these are far less so than those of Cuvier’s Discours. He distinguishes between the action of rivers or of fresh-water currents, torrents, storms, the melting of snow, and the work of the ocean. The rivers wear away and bear materials from the highlands to the lowlands, so that the plains are gradually elevated; ravines form and become immense valleys, and their sides form elevated crests and pass into mountain ranges.

He brings out and emphasizes the fact, now so well known, that the erosive action of rain and rivers has formed mountains of a certain class.

“It is then evident to me, that every mountain which is not the result of a volcanic irruption or of some local catastrophe, has been carved out from a plain, where its mass is gradually formed, and was a part of it; hence what in this case are the summits of the mountains are only the remains of the former level of the plain unless the process of washing away and other means of degradation have not since reduced its height.”

Now this will apply perfectly well to our table-lands, mesas, the mountains of our bad-lands, even to our Catskills and to many elevations of this nature in France and in northern Africa. But Lamarck unfortunately does not stop here, but with the zeal of an innovator, by no means confined to his time alone, claims that the mountain masses of the Alps and the Andes were carved out of plains which had been raised above the sea-level to the present heights of those mountains.

Two causes, he says, have concurred in forming these elevated plains.

“One consists in the continual accumulation of material filling the portion of the ocean-basin from which the same seas slowly retreat; for it does not abandon those parts of the ocean-basin which are situated nearer and nearer to the shores that it tends to leave, until after having filled its bottom and having gradually raised it. It follows that the coasts which the sea is abandoning are never made by a very deep-lying formation, however often it appears to be such, for they are continually elevated as the result of the perpetual balancing of the sea, which casts off from its shores all the sediments brought down by the rivers; in such a way that the great depths of the ocean are not near the shore from which the sea retreats, but out in the middle of the ocean and near the opposite shores which the sea tends to invade.

“The other cause, as we shall see, is found in the detritus of organic bodies successively accumulated, which perpetually elevates, although with extreme slowness, the soil of the dry portions of the globe, and which does it all the more rapidly, as the situation of these parts gives less play to the degradation of the surface caused by the rivers.

“Doubtless a plain which is destined some day to furnish the mountains which the rivers will carve out from its mass would have, when still but a little way from the sea, but a moderate elevation above its river channels; but gradually as the ocean basin removed from this plain, this basin constantly sinking down into the interior (épaisseur) of the external crust of the globe, and the soil of the plain perpetually rising higher from the deposition of the detritus of organic bodies, it results that, after ages of elevation of the plain in question, it would be in the end sufficiently thick for high mountains to be shaped and carved out of its mass.

“Although the ephemeral length of life of man prevents his appreciation of this fact, it is certain that the soil of a plain unceasingly acquires a real increase in its elevation in proportion as it is covered with different plants and animals. Indeed the débris successively heaped up for numerous generations of all these beings which have by turns perished, and which, as the result of the action of their organs, have, during the course of this life, given rise to combinations which would never have existed without this means, most of the principles which have formed them not being borrowed from the soil; this débris, I say, wasting successively on the soil of the plain in question, gradually increases the thickness of its external bed, multiplies there the mineral matters of all kinds and gradually elevates the formation.”

Our author, as is evident, had no conception, nor had any one else at the time he wrote, of the slow secular elevation of a continental plateau by crust-movements, and Lamarck’s idea of the formation of elevated plains on land by the accumulation of débris of organisms is manifestly inadequate, our aërial or eolian rocks and loess being wind-deposits of sand and silt rather than matters of organic origin. Thus he cites as an example of his theory the vast elevated plains of Tartary, which he thought had been dry land from time immemorable, though we now know that the rise took place in the quaternary or present period. On the other hand, given these vast elevated plains, he was correct in affirming that rivers flowing through them wore out enormous valleys and carved out high mountains, left standing by atmospheric erosion, for examples of such are to be seen in the valley of the Nile, the Colorado, the Upper Missouri, etc.