PRESIDENT'S ADDRESS. Ixv. 



many -well-known genera arc taken at the greatest depths, so that 

 the enormous pressure, the utter darkness, and the differences in 

 the chemical and physical conditions of the water do not influence 

 animal life to any great extent. The geographical extension of any 

 species appears to depend mainly upon the maintenance of a 

 tolerably uniform temperature and an adequate supply of suitable 

 food. No plants live at great depths in the sea ; what is usually 

 understood by vegetation is practically limited to depths less than 

 100 fathoms. Very few of the higher algze live even occasionally 

 on the surface of the sea. The exception is the gulf-weed 

 (Sargassum bacciferum). Confervoids and unicellular algse do 

 occur occasionally, and sometimes in such profusion as to discolour 

 the water over an area of many miles. Diatoms are found on the 

 surface in abundance, their frustules occur in all deep water 

 deposits. The foraminifera and radiolarians behave in a similar 

 manner, occurring on the surface and in the intermediate water. 

 . The deep-sea deposits of the foraminifera contain over 40 per cent, 

 of carbonate of lime, consisting principally of their dead shells. In 

 some localities the percentage is as high as 95 per cent. The 

 deep-sea diatom-deposits contain on an average about 25 per cent. 

 of carbonate of lime. 



In 1857 Captain Dayman sounded across the North Atlantic 

 between Valencia and Newfoundland. The soundings were 

 examined by the late Professor Huxley, who found them composed 

 mainly of the dead shells of pelagic foraminifera (globigerina, &c.), 

 and considered them of high scientific value on account of their 

 depth. There can be no doubt that there is a vast sheet of rock 

 forming at the bottom of the present ocean which closely resembles 

 chalk, and there can be as little doubt that the Cretaceous forma- 

 tion, which in some parts of England has been subjected to 

 enormous denudation, was produced in the same manner and under 

 closely similar circumstances. In almost all of these the remains 

 of Foraminifera are abundant, some of them apparently specifically 

 identical with living forms. There are, however, important 

 differences between the chalk of the Cretaceous period and the 



