42 THE POPULAR SCIENCE MONTHLY. 



ceans, testaceans, and polyps, mixed with sand, and to a great ex- 

 tent petrified. This crust may be seven or eight feet deep, and he 

 attributed to this deposit, bound together with the remains of or- 

 ganisms and sedimentary mineral matter, the rising of the bot- 

 tom of the sea, and the encroachment of the water on the coasts. 



In 1836 Ehrenberg produced the first of a long series of publi- 

 cations 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 ma- 

 terials 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 radio- 

 laria, and having found living diatoms and radiolaria on the sur- 

 face of the Baltic of the same species as those found in the Ter- 

 tiary deposits of Sicily, and having shown that in the diatom layers 

 of Bilin in Bohemia the siliceous deposit had, under the influ- 

 ence of infiltrated water, been transformed into compact opaline 

 masses, he concluded that rocks like those which play so impor- 

 tant a part in the terrestrial crust are still being formed on the 

 bottom of the sea. 



The investigation of the distribution of marine animals accord- 

 ing 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 suc- 

 cessive depths, having each a special association of species ; and 

 remarks that the speciea 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- 



