areas referred to, one vast sheet of ice, originating in the higher Alps, had extended over the entire valley of north-western Switzerland until it reached the southern slopes of the Jura, which, though they checked and deflected its further extension, did not prevent the ice from reaching in many places the summit of the range. The publication of this work gave a fresh impetus to the study of glacial phenomena in all parts of the world.
Thus familiarized with the phenomena attendant on the movements of recent glaciers, Agassiz was prepared for a discovery which he made in 1840, in conjunction with William Buckland. These two savants visited the mountains of Scotland together, and found in different localities clear evidence of ancient glacial action. The discovery was announced to the Geological Society of London in successive communications from the two distinguished observers. The mountainous districts of England and Wales and Ireland were also considered to constitute centres for the dispersion of glacial débris; and Agassiz remarked “that great sheets of ice, resembling those now existing in Greenland, once covered all the countries in which unstratified gravel (boulder drift) is found; that this gravel was in general produced by the trituration of the sheets of ice upon the subjacent surface, &c.”
In 1842–1846 he issued his Nomenclator Zoologicus, a classified list, with references, of all names employed in zoology for genera and groups—a work of great labour and research. With the aid of a grant of money from the king of Prussia, Agassiz, in the autumn of 1846, crossed the Atlantic, with the twofold design of investigating the natural history and geology of the United States and delivering a course of lectures on zoology, by invitation from J. A. Lowell, at the Lowell Institute at Boston; the tempting advantages, pecuniary and scientific, presented to him in the New World induced him to settle in the United States, where he remained to the end of his life. He was appointed professor of zoology and geology in Harvard University, Cambridge, U.S., in 1847. In 1852 he accepted a medical professorship of comparative anatomy at Charles town, but this he resigned in two years.
The transfer to a new field and the association with fresh objects of interest gave his energies an increased stimulus. Volume after volume now proceeded from his pen: some of his writings were popular, but most of them dealt with the higher departments of scientific research. His work on Lake Superior, and his four volumes of Contributions to the Natural History of the United States, 1857–1862, were of this latter character. We must not overlook the valuable service he rendered to science by the formation, for his own use, of a catalogue of scientific memoirs—an extraordinary work for a man whose hands were already so full. This catalogue, edited and materially enlarged by the late Hugh E. Strickland, was published by the Ray Society under the title of Bibliographia Zoologiae et Geologiae, in 4 vols., 1848–1854. Nor must we forget that he was building up another magnificent monument of his industry in the Museum of Natural History, which rose under his fostering care, at Cambridge. But at length the great strain on his physical powers began to tell. His early labours among the fishes of Brazil had often caused him to cast a longing glance towards that country, and he now resolved to combine the pursuit of health with the gratification of his long-cherished desires. In April 1865 he started for Brazil, with his wife and class of qualified assistants. An interesting account of this expedition, entitled A Journey in Brazil (1868), was published by Mrs Agassiz and himself after they returned home in August 1866.
In 1871 he made a second excursion, visiting the southern shores of the North American continent, both on its Atlantic and its Pacific sea-boards. He had for many years yearned after the establishment of a permanent school where zoological science could be pursued amidst the haunts of the living, subjects of study. The last, and possibly the most influential, of the labours of his life was the establishment of such an institution, which he was enabled to effect through the liberality of Mr John Anderson, a citizen of New York. That gentleman, in 1873, not only handed over to Agassiz the island of Penikese, in Buzzard’s Bay, on the east coast, but also presented him with $50,000 wherewith permanently to endow it as a practical school of natural science, especially devoted to the study of marine zoology. Unfortunately he did not long survive the establishment of this institution. The disease with which he had struggled for some years proved fatal on the 14th of December 1873. He was buried at Mount Auburn. His monument is a boulder selected from the moraine of the glacier of the Aar near the site of the old Hôtel des Neuchâtelois, not far from the spot where his hut once stood; and the pine-trees which shelter his grave were sent from his old home in Switzerland. His extensive knowledge of natural history makes it somewhat remarkable to find that from first to last he steadily rejected the doctrine of evolution, and affirmed his belief in independent creations. When studying the superficial deposits of the Brazilian plains in 1865, his vivid imagination covered even that wide tropical area, as it had covered Switzerland before, with one vast glacier, extending from the Andes to the sea. This view, however, has not been generally accepted. His daring conceptions were only equalled by the unwearied industry and genuine enthusiasm with which he worked them out; and if in details his labours were somewhat defective, it was only because he had ventured to attempt what was too much for any one man to accomplish.
It may be interesting to mention that the charming verses written by Longfellow on “The fiftieth birthday of Agassiz” were read by the author at a dinner given to Agassiz by the Saturday Club in Cambridge, Mass., in 1857.
Louis Agassiz was twice married, and by his first wife he had an only son, Alexander Agassiz (q.v.), born in 1835; in 1850, after her death, he married his second wife, Elizabeth Cabot Cary of Boston, Mass., afterwards well known as a writer and as an active promoter of educational work in connexion with Radcliffe College (see an article on Radcliffe College, by Helen Leah Reed in the New England Magazine for January 1895).
Authorities.—L. Agassiz, His Life and Correspondence, 2 vols., by E. C. (Mrs) Agassiz (London, 1885); Louis Agassiz, His Life and Work, by C. F. Holder (New York and London, 1893). (H. B. Wo.)
AGATE, a term applied not to a distinct mineral species, but to an aggregate of various forms of silica, chiefly Chalcedony (q.v.). According to Theophrastus the agate (ἀχάτης) was named from the river Achates, now the Drillo, in Sicily, where the stone was originally found. Most agates occur as nodules in eruptive rocks, or ancient lavas, where they represent cavities originally produced by the disengagement of vapour in the molten mass, and since filled, wholly or partially, by siliceous matter deposited in regular layers upon the walls. Such agates, when cut transversely, exhibit a succession of parallel lines, often of extreme tenuity, giving a banded appearance to the section, whence such stones are known as banded agate, riband agate and striped agate. Certain agates also occur, to a limited extent, in veins, of which a notable example is the beautiful brecciated agate of Schlottwitz, near Wesenstein in Saxony—a stone mostly composed of angular fragments of agate cemented with amethystine quartz.
In the formation of an ordinary agate, it is probable that waters containing silica in solution—derived, perhaps, from the decomposition of some of the silicates in the lava itself—percolated through the rock, and deposited a siliceous coating on the interior of the vapour-vesicles. Variations in the character of the solution, or in the conditions of deposit, may have caused corresponding variation in the successive layers, so that bands of chalcedony often alternate with layers of crystalline quartz, and occasionally of opaline silica. By movement of the lava, when originally viscous, the vesicles were in many cases drawn out and compressed, whence the mineral matter with which they became filled assumed an elongated form, having the longer axis in the direction in which the magma flowed. From the fact that these kernels are more or less almond-shaped they are called amygdales, whilst the rock which encloses them is known as an amygdaloid. Several vapour-vesicles may unite while the
