ceans, testaceans, and polyps, mixed with sand, and to a great extent petrified. This crust may be seven or eight feet deep, and he attributed to this deposit, bound together with the remains of organisms and sedimentary mineral matter, the rising of the bottom of the sea, and the encroachment of the water on the coasts.
In 1836 Ehrenberg produced the first of a long series of publications relating to microscopic organisms which distinguished him as a naturalist of rare sagacity. He devoted the whole of his life to the study of microscopic organisms, to the examination of materials brought up from deep-sea soundings, and to all questions appertaining to the sea. Having discovered that the siliceous strata known as tripoli, found in various parts of the globe, are but accumulations of the skeletons of diatoms, sponges, and radiolaria, and having found living diatoms and radiolaria on the surface of the Baltic of the same species as those found in the Tertiary deposits of Sicily, and having shown that in the diatom layers of Bilin in Bohemia the siliceous deposit had, under the influence of infiltrated water, been transformed into compact opaline masses, he concluded that rocks like those which play so important a part in the terrestrial crust are still being formed on the bottom of the sea.
The investigation of the distribution of marine animals according to the depths of the sea may be said to have commenced in 1840 with Forbes's studies in the Mediterranean. He maintained that the dredgings showed the existence of distinct regions at successive depths, having each a special association of species; and remarks that the species found at the greatest depths are also found on the coast of England—concluding, therefore, that such species have a wider geographical distribution. He divided the whole range of depth occupied by marine animals into eight zones, in which animal life gradually diminished with increase of depth, until a zero was reached at about three hundred fathoms. He also supposed that plants, like animals, disappeared at a certain depth, the zero of vegetable life being at a less depth than that of animal life.
It has already been mentioned that probably the first reliable deep-sea soundings ever made were by Sir John Ross in 1818. To him is due the invention of the so-called deep-sea clam, by means of which specimens of the bottom were for the first time brought up from great depths in any quantity. This instrument was in the form of a pair of spoon-forceps, kept apart while descending, but closed by a falling weight on striking the bottom. Two separate casts were usually made, one to ascertain the depth and the other to bring up a specimen of the bottom soil.
For the development of accurate knowledge of the depths of the sea the world will ever be indebted to the genius of Midship-
