hundred species, the counterparts of which are to be found in the great museums in Europe, and has thus become one of the most precious documents we possess concerning this class of animals.

The labors of Mr. Agassiz on Fossil Shells are not less important. A young Swiss geologist, M. Gressly, had made a considerable collection of fossil shells from all the stages of the oolitic and cretaceous formations. Mr. Agassiz commenced the publication of them in a work entitled "Etudes critiques sur les Mollusques fossiles du Jura et de la Craie." Of this, four numbers have appeared, with a hundred quarto plates, comprising the group of the Trygonia and that of the Myo. At the same time Agassiz published a German translation of Buckland's Geology, with numerous notes and additions, and revised the French and German translations of Sowerby's Mineral Conchology.

But whatever may be any man's ability and energy, Nature has fixed certain limits to what it is possible for him to accomplish, which he cannot pass. Thus, in order to explain the rapid succession, at so short intervals, of the works we have mentioned, and those of which we have yet to speak, we must observe, that about this time, (1837,) Agassiz associated with. himself a young naturalist, Mr. Desor,-who has ever since labored with him and under his direction, and who, having accompanied him in all his Alpine excursions, and in his visit to this country, is now living among us. To the information personally furnished by Mr. Desor, as well as to his writings, we are indebted for much of the present sketch, which could not have been written without his assistance.

The united labors of the two friends accomplished what would have been beyond the reach of a single individual, and the fruits of these labors we see in these numerous publications.

The reputation of Mr. Agassiz, and his unwearying energy, transformed the little town of Neufchatel into a nursery of science to the great astonishment of the peaceful burghers, who, for the most part, could not at all comprehend what was going on around them. But the more enlightened among them soon gathered about him, and thus a Society of Natural History was formed, that soon drew attention by its activity. The Museum, established by the liberality of some of the citi zens, increased rapidly. At the recommendation of Mr. Agassiz, a young naturalist, a pupil of his, Mr. Tschudi,

since known by his work on Peru, -was despatched on a voyage round the world, to collect objects of Natural History.

The influence which Agassiz exercised was not confined to the town where he lived. He succeeded also in reviving the zeal of the "Société Helvétique des Sciences Naturelles," of which he was one of the directors. It was in consequence of his exertions that this society resumed with renewed vigor its publications, which had languished for some time for want of nourishment.

His studies of the Fossils did not make Agassiz forget the Fishes, which have always been, and still are, his favorites. He continued to collect materials for his "Natural History of the Fresh-water Fishes of Europe." His portfolios now contained a complete series of drawings, executed with the greatest care by Mr. Dinkel, the skilful draughtsman whom he had educated at Munich. Having formed at Neufchatel a lithographic establishment, in which there were several distinguished artists, he determined to commence the publication of his work. The plates of the magnificent Atlas-which justly ranks among the first works in this department"--were struck off under his eye at Neufchatel. It is on this account only the more to be regretted, that, after having exhausted all his pecuniary resources, to make this publication worthy of its name, the author found it impossible to continue it on the plan projected. Nevertheless, science has been partly indemnified by the publication of the Embryology of the Salmon tribe, which forms the second number of the work.

After the attention which German naturalists had given to the study of this important and interesting branch of science, Agassiz determined that his Fishes also should contribute their share. He therefore employed his friend, Mr. Vogt, (now Professor of Zoology at the University of Giessen,) who, under his direction, elaborated this part of the work, which is justly esteemed by all physiologists. A third part of the same work, -the Anatomy of the Salmons, -the fruit of the joint labors of Messrs. Agassiz and Vogt, has since appeared in the third volume of the Memoirs of the Neufchatel Society, with a large number of admirably executed plates.

Mr. Agassiz had finished the publication of the "Fossil

We may add, that, in the opinion of Mr. Agassiz, the execution of these plates has been surpassed only in one work, the Ichthyology of the United States Exploring Expedition.

Fishes." But though the book was finished, the subject was not exhausted. Numerous contributions poured in from all quarters. The study of the Devonian system, in particular, had made known a whole ichthyological fauna of a peculiar character. Mr. Agassiz was requested by the British Association to publish these interesting remains. This he did in a First Supplement to the "Poissons Fossiles"-under the name of the "Fishes of the Devonian System." About the same time he presented to the British Association his Report on the Fishes of the London Clay.

After the publication of the "Fresh-water Fishes," there appeared a work of a different character, and which of itself would be sufficient to establish the reputation of a naturalist. This is the Nomenclator Zoologicus"-an enumeration of all the genera in the animal kingdom, with an indication of the etymology of their names,-of the author by whom the names were proposed, -the date of their publication,-and the family to which they should be referred.

From the commencement of his career, Agassiz had been struck by the disorder that pervaded zoological nomenclature, and the confusion resulting from the application of the same name to totally different animals. To remedy this difficulty, he prepared registers, in which he entered the names of all animals as they occurred to him in his studies. After having continued this practice for more than ten years, he arranged the names methodically, and published the nomenclature of each class separately, after having it revised by the naturalists most distinguished throughout Europe in each special branch. The Nomenclator Zoologicus is preceded by an introduction in Latin, in which the general principles of nomenclature are profoundly discussed, and it has become an authority universally acknowledged. In connection with this work we must mention another publication, more extensive and not less important the "Bibliographie générale d'histoire naturelle;" which grew up in a similar manner by the side of the Nomenclator. It contains a list of the authors cited in the former work, with bibliographical notices, and is in course of publica tion, at the expense of the Ray Society. This work will form several large volumes;-the first numbers, containing a list of the publications of scientific institutions, have recently appeared.

We come now to speak of a series of discoveries which have particularly tended to make the name of Agassiz known to the

public in general, and from which resulted his Glacial theory. This theory is so generally known, that it may be interesting to relate, in a few words, its origin and the different phases in which it has appeared. Although now of so wide application, (extending to the whole northern hemisphere, as far as erratic boulders and polished rocks are found,) its first origin is to be sought in the Alps. It was among the chamois-hunters of the Valais that the idea arose, that masses of rock were transported by glaciers. These men, accustomed to live in the high regions of the Alps, and seeing every year enormous masses of rock transported to a distance from their original position by the glaciers, found no difficulty in supposing that all the boulders which are found in the valleys had been transported thither in the same manner; and as they had observed the oscillation of the extremities of the glaciers,-that is to say, their advance in one year and their recession in the next,they concluded, in like manner, that, at the period when the blocks now found at a distance from the glaciers were first detached, the glaciers themselves must have reached further than at present.

These notions, however, had not extended beyond the limits of the Alpine valleys. M. Venetz, an engineer of the Valais, was the first to undertake an application of them, in a treatise on the subject, in which he showed, that at various periods since the end of the last century the glaciers had extended further than at present, and in retiring had left everywhere heaps of stones and large rocks, as marks of their presence. Afterwards, M. de Charpentier conceived the idea of extending the application of these facts beyond the region of the present glaciers. He advanced the hypothesis, that the distribution of the boulders which are scattered over the valley of Switzerland and on the sides of the Jura, may be accounted for in this way. This opinion, which he expressed in a brief treatise, was received with almost unanimous incredulity; so generally adopted was Saussure's theory, which accounted for these phenomena by the supposition that the Alpine chain had formerly been broken through at various points, allowing vast lakes, before shut up within its walls, to escape with violence.†

The northern part of Switzerland, between the Bernese Oberland and the Jura, goes by this name.

† For some account of Saussure's theory see Lyell's Elements of Geology, American edition, Vol. I., p. 245.

Mr. Agassiz, as we hear, was among the skeptics, and, in 1836, visited M. de Charpentier, with the view of persuading his friend to relinquish an hypothesis which he considered untenable. But the latter, instead of entering into a discussion, conducted Agassiz to the places themselves, on the Mer de Glace, at Chamouni, where his observations had been made. He showed him the glacier actually at work in transporting boulders, and in its passage polishing and rounding the rocks at its sides. A light now burst upon the mind of Mr. Agassiz: not only did he admit that the blocks found in the valley of Switzerland might have been carried thither in this manner, but he saw moreover at a glance the immense bearing of this fact, and the effect it must necessarily have on the science of Geology.

And indeed, in order that the Alpine glaciers should extend to the Jura, so as to deposit these blocks at the elevation of four thousand feet, the valley of Switzerland must have been covered with ice at least two thousand five hundred feet thick. Now such an accumulation of ice could not be the effect of a local cause. The depression of temperature necessary to account for this extension of these glaciers, must have made itself felt elsewhere, and this with an intensity increasing towards the north. Now as the soil of Scandinavia presents the same marks of friction as the sides of the Alps and the Jura, accompanied also by erratic boulders, the conclusion was deduced, that all the north of Europe must have been covered by a vast sheet of ice, in the same manner as the polar regions are at present. The formation of this sheet of ice, in consequence of a sudden depression of the temperature, it was insisted, must have put an end to the tertiary epoch, by annihilating the animals and plants then existing.

Such was the original form of the Glacial Theory, which was first announced in a discourse of Mr. Agassiz, in 1837, at the opening of the meeting of the Société Helvétique, held at Neufchatel. The opposition excited by M. de Charpentier's theory, (which only extended the glaciers of the Alps as far as the Jura,) was roused in a tenfold degree by that of Mr. Agassiz. As is always the case when a new truth dawns upon the world, two parties were immediately formed; one embracing the new doctrine with enthusiasm, the other furiously opposing it. Disputes arose even concerning the present glaciers. It was denied that they were capable of polishing and scratching rocks. Doubts were raised as to the mode in which they advanced, and as the very fact of their advance rested