liv PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



as they grew, or ripple-marked sandstones and sandy or gravelly strata 

 with subordinate diagonal layers, confirm these views. Such move- 

 ments took place contemporaneously with the growth of organic mat- 

 ter, just as subsidence on a grand scale is now going on over vast 

 areas in the Pacific and Indian Oceans, — a class of facts on which 

 Mr. Darwin has founded his theory of atolls, or the origin of annular 

 coral islands with lagoons. His theory, as you have probably ob- 

 served, has been recently embraced and more fully elucidated by 

 Mr. Dana, in his valuable chapters on the geology of the American 

 Exploring Expedition under Capt. Wilkes. 



The investigations of Professor Edward Forbes, on the laws go- 

 verning the distribution of marine animal hfe, at various depths in 

 the jMediterranean, have powerfully aided us in determining the con- 

 ditions under which particular strata were formed, the depth of water 

 being deducible from a careful study of the organic contents of each 

 bed. Availing themselves of this key, Captam Ibbetson and Profes- 

 sor Forbes have shown how the lower cretaceous strata of the Isle of 

 Wight have been deposited on a gradually sinking submarine bottom, 

 while Mr. Prestwich has apphed the same method of reasoning, with 

 equal success, to the eocene strata of Alum and Whitecliff Bays in the 

 same island*. In this instance it is remarkable, that after a depres- 

 sion of 1800 feet very slowly effected, there was still contiguous land 

 inhabited by the Palseothere of Binstead and Hordwell and its 

 contemporaries, as well as a freshwater estuary, implying that the 

 movements in different parts of that region were either very unequal 

 or opposite, or that they consisted of great oscillations of level. It 

 would be easy to cite a variety of continental authorities in support 

 of the same principle, but enough has been stated to entitle me to ask, 

 whether the subsidence of mountainous masses, lying immediately 

 beneath the floor of the ocean, brought about by such slow degrees, 

 can possibly occur, without causing beneath many of the sunk areas, 

 vast flexures of the strata, which as they smk for miles vertically must 

 occasionally be forced to pack themselves into smaller spaces than 

 those which they previously occupied. If this be true, the contortions 

 and foldings of pliant beds, and the fracture and dislocation of the 

 more unyielding rocks, have frequently been due to movements as 

 gradual as those of various ages to which I have been alluding. 

 * Prestwich, Quart. Journ. Geol. Soc. vol. ii. p. 223. 



