Page:The American Cyclopædia (1879) Volume VI.djvu/267

 DREDGING (DEEP-SEA) 259 of a track for the submarine telegraph between Key West, Florida, and Havana. Although but a few casts were obtained in that year, and the depths reached did not exceed 500 fathoms, the results were so promising that dredgings were carried out systematically over the region comprised between the Florida reef and the axis of the straits of Florida, with occasional extensions to the coast of Cuba and the Bahama banks, during the two following years. This is probably at this time the only example of a connected dredging survey of a defined submarine region. The results estab- lished several well defined zones characterized by peculiar faunae, the animals comprising them being generally new discoveries, or in several cases known only from high northern latitudes, thus bearing out in part Loven's theory that beyond a certain depth the ocean is peopled by a fauna, extending from pole to pole. In these explorations the greatest depths reached were about 700 fathoms. One of the most notable examples of an animal found in Florida and off the northern coast of Norway is the little crinoid rhizocrinus Lofottensis, discov- ered the year previous by Sars. This seems to have been one of the principal incentives in determining the fitting out of the deep-sea dredging expeditions of the Lightning and Porcupine by the British government, under the direction of Profs. W. Thomson and W. B. Carpenter. The first cruise in the Lightning was made in 1868, between the British and the Faroe islands, with very promising results. The next year the Porcupine was employed on the same service, off the W. and S. W. coasts of Ireland. The depth of 2,435 fathoms was attained by the dredge, which brought up quite a variety of living animals, ranging from mol- lusks and Crustacea downward. During the following summer the same researches were extended across the bay of Biscay, along the coast of Portugal, and into the Mediterranean, with great success generally, though in the latter sea the greater depths were found sin- gularly barren, probably on account of the want of circulation in the water. (See AT- LANTIC OCEAN.) The British government was induced by the general interest which these researches had created to fit out a large ship, the Challenger, for a cruise of deep-sea explo- ration on a large scale, which in 1872 started, under the scientific leadership of Prof. W. Thomson, on a voyage of circumnavigation. In the earlier part of the voyage, in the At- lantic, the dredge was used with success in the depth of 3,895 fathoms. A few deep-sea casts were also made during the voyage of the United States steamer Hassler from Boston to San Francisco in 1872, but did not attain so great a depth. In 1871 the United States fishery commission, directed by Prof. S. F. Baird, made extensive explorations of the sea bottom on the coast of New England, Prof. Verrill and Dr. Packard having charge of the dredging operations. Deep-sea dredgings were made off St. George's bank and in the gulfs of Maine comprised between Cape Cod and Cape Sable. The fauna, as might have been expect- ed, was entirely arctic, with the exception of a single specimen of a small coral, deltocyathua, a West Indian deep-sea form, the presence of which north of Florida had not been detected before. Dredging in deep water has greatly increased our knowledge of the animal world, and precisely at a time when the need of such a knowledge is most keenly felt. The great bed of foraminifera has already been mentioned. A gelatinous matter pervades this bed in most localities, which under the microscope seems to be endowed with a kind of motion or change of form, and has thence been raised to the dig- nity of a living organism under the name of lathylius Haclcelii by Huxley. Its nature is really as yet but imperfectly understood. The same may be said of small calcareous bodies which have been named coccoliths. (See BA- THYBITJS, and COCCOLITHS AND COCCOSPHERES.) The sponges are represented by a number of forms, having generally a beautiful silicious skeleton. Then come a considerable number of small corals, generally simple. The echino- derms are abundant and peculiar ; among them the most notable are the crinoids. The rhizo- crinus Lofottensis has been found in the straits of Florida and in the seas of Europe. An- other species has been recently discovered in the West Indies by the Hassler expedition, in company with two species of pentacrinus and the remarkable holopus. Another pentacrinus and bathycrinus gracilis belong to the Euro- pean seas. The sea urchins or eehinidce of great depths are very remarkable, and among them several genera are represented much more nearly related to forms of the cretaceous or early tertiary period than to any recent ones. Of the mollusks we know less than of the other classes ; partly because the collections of the American dredging expeditions were lost in the great fire of Chicago, and partly because the English collections have not yet been fully worked up. What we know at present points to the same conclusions as derived from other branches of the animal kingdom. Deep-sea researches are also extending the science of geology, particularly as it refers to sedimentary rocks. The dredgings off the Florida reef brought up large fragments of limestone rock in process of formation, and of different grades of compactness, formed by the various mol- lusks, bryozoa, serpulae, corals, foraminifera, &c., still living on its surface. On other parts of our southern coast we have the beds of foraminifera gradually undergoing transfor- mation into glauconite or greensand, such as we find in the tertiary formation of New Jersey. This process, as yet unexplained, takes place in comparatively limited locali- ties, while the great bed of foraminifera be- comes compacted without alteration into a formation almost identical with the white chalk; and the continuity of that formation