A G A A G A 977 extraordinary work for a man whose hands were already so full. This catalogue, edited and materially enlarged by the late Hugh Strickland, was published by the Ray Society under the title of Biblingraphia Zoologies et Geo- loffice. Nor must we forget that he was building up another magnificent monument of his industry in the Museum of Natural History, Avhich rose under his foster ing care, at Cambridge. But at length the great strain on his physical powers began to tell. He then sought to restore his waning health by a southern voyage. 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 18G5 he started for Brazil, along with his admirable wife and an excellent class of assistants. Even on shipboard he could not be idle. In his outward voyage he delivered a course of lectures, open to all his fellow-passengers, but especially addressed to his assistants, and intended to instruct them in the nature and bearings of the great problems iipon which they might hope to throw light during their stay in Brazil. An interesting account of this journey, to the success of which the emperor of Brazil contributed in every possible way, was published by Mrs Agassiz when they returned home, laden with the natural treasures of the Brazilian rivers. In 1871 he made a second excursion, visiting the southern shores of the North American continent, both on its Atlantic and its Pacific seaboards. He had for many years yearned after the establishment of some permanent school where zoological science could be studied, not in class-rooms or museums of dead specimens, but amidst the living haunts of the subjects of study. Like all truly great teachers, he had little faith in any school but that of nature. The last, and possibly the most permanently in fluential, of the labours of his long and successful 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 not only handed over to Agassiz the island of Penikese, on the east coast, but also presented him with $50,000 wherewith per manently to endow it as a practical school of natural science, especially devoted to the study of marine zoology. Another American friend gave him a fine yacht, of 80 tons burden, to be employed in marine dredging in the sur rounding seas. Had Agassiz lived long enough to bring all this machinery into working order, it is difficult to ex aggerate the practical advantages which American science would have reaped from it when guided by such experi enced hands. But it was otherwise ordained. The disease with which he had struggled for some years proved fatal on Dec. 14, 1873. A letter to his old friend, Sir Philip M. de Grey Eger- ton, Bart., written but a few days before his death, and doubtless one of the last that he penned, showed that his spirit was still as indomitable and his designs as large as ever; and one of his latest expressed wishes was that he might be spared for four more years in order that the work he had contemplated might be completed. Our available space will not allow us to give a de tailed sketch of the opinions of this remarkable man on even the more important of the great subjects which he studied so long. From first to last he steadily rejected the doctrine of evolution, and affirmed his belief in inde pendent creations. In like manner he retained his confi dence in the former existence and agency of vast continental ice-sheets, rather than in the combined action of more limited glaciers and icebergs, which nearly all modern geologists recognise as the producers of the drifts and boulder-clays. 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. 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 some what defective, it was only because he had the courage to attempt what was too much for any one man to accom plish, (w. c. w.) AGATE (from Achates, a river in Sicily, on the banks of which it is said to have been found), a name applied by mineralogists to a stone of the quartz family, generally occurring in rounded nodules or in veins in trap rocks. The number of agate balls in the rock often give it the character of amygdaloid; and when such a rock is decom posed by the elements, the agates drop out, and are found in the beds of streams that descend from it; or they may be obtained in quarrying. Great quantities are obtained from Oberstein and Idar, in Germany, where there are large manufactories for colouring and polishing the stones; and many are brought from India and Brazil. Agate occurs in considerable quantity in Scotland, whence the stone is familiarly known to lapidaries as Scotch pebble; and very large masses of calcedony, a variety of it, are brought from Iceland, the Faroe Islands, and Brazil. Agate chiefly con sists of calcedony, with mixtures of common quartz and occasional patches of jasper and opal. The colour markings are often in concentric rings of varying forms and inten sity, or in straight parallel layers or bands. The colours are chiefly gray, white, yellow, or brownish-red. The com position of agate is not uniform; but it usually contains from 70 to 96 per cent, of silica, with varying proportions of alumina, coloured by oxide of iron or manganese. The principal varieties arc 1. Calcedony. In this the colours are in parallel bands. The porosity of this stone, and the presence of iron in it, have given rise to a beautiful artificial process for height ening its natural colours, which has been long practised at Oberstein, and probably long known in India. The stones best suited for this purpose are such as when recently frac tured imbibe moisture most readily. The stones are first dried without heat, then immersed in a mixture of honey and water, and afterwards placed in a heated oven, Avhere they remain for two or three weeks, constantly covered with the liquid. They are then washed, dried, and put into an earthenware vessel containing sufficient sulphuric acid to cover them ; this vessel is closed and placed in the oven for a space varying from one to twelve hours, according to the hardness of the stone. The agates are now removed, washed, and thoroughly dried; and after being kept in oil for twenty- four hours, are cleaned, cut, and polished. In the best specimens the gray streaks are increased in intensity; some exhibit brown streaks approaching to black, while white impenetrable parts assume a brighter hue by the contrast. This is the process employed to convert the veined calce dony or agate into onyx, especially for the production of cameos and intaglios, in imitation of the antique sculptured gems, of which admirable specimens are found in the cabinets of the curious, and especially in the Florentine Museum. In those minute but exquisite works the ancient Greeks espe cially excelled; and remarkable specimens of the art have been found in the tombs of Egypt, Assyria, and Etruria. In such works the figures, whether in relief or intaglio, appear of a different colour from the ground. 2. Carnelian, or red calcedony, when found, is almost always brownish or muddy. The following process is employed at Oberstein to convert both this sort and the yellowish-brown varieties into a rich red, so as to rival the Indian carnelian, which probably also has its colour
heightened artificially : After being thoroughly dried, the
