612 DYNAMICAL GEOLOGY. 



contain numerous, long, slender, white and yellow vegetable fibres, on undetermined 

 relations, waving in the boiling eddies, and becoming buried in the siliceous deposits 

 over the bottom, where they often form layers several inches thick. The bright green 

 forms appear to be confined to lower temperatures. W. R. Taggart reports that, at 

 the vents on the shores of Lewis's Lake, leafy vegetation is limited to temperatures 

 below 120°. (Hayden's Reports, 1871-2.) Dr. Josiah Curtis found, in these hot springs, 

 siliceous skeletons of very numerous Diatoms; but the vegetable matter was wanting, 

 in all cases, where the temperature exceeded 96° F. So many different causes might 

 introduce these skeletons to the hotter pools, that their presence has not necessarily 

 any more significance than that of the grasshoppers and butterflies which are frequently 

 found in the same pools. Living larves of Helicopsyche were found, by Mr. Taggart, 

 in a spring having the temperature of 180°, into which, however, they might have 

 crawled from the river, which was close by; so that the eggs were not necessarily laid 

 at the temperature given. 



At Bafios. on Luzon, Phillippine Islands, the author observed feathery Confervse, in 

 waters heated to 160° F. 



3. By light. — Species are sometimes subterranean, and have pecu- 

 liarities depending on the absence of light, being without sight, as 

 with the blind Fish and Crustaceans of the Mammoth Cave, etc. 



4. By freedom from rough mechanical agents, and the reverse. — The 

 occurrence of the siliceous sponges especially over the bed of the deep 

 oceans, has been accounted for on the view that they are too delicate 

 to exist where there is much movement in the waters. On the other 

 hand, some Corals and other species seem to thrive best amid the 

 breakers. 



5. By the character of the bottom or shores, whether rocky, sandy, or 

 muddy. 



2. The nature of different organic products, and the fitness of the 

 species affording them for making fossils and rocks. 



(a.) Nature of the organic products contributed to rock-formations. — 

 Some of the general facts, relating to the nature of the organic prod- 

 ucts contributed by Life to the rocks, are mentioned on pages 59 to 

 62. The following are additional facts : — 



Plants afford, besides carbon, oxygen, hydrogen, potash, and soda, with some sul- 

 phur and nitrogen. Carbonic acid is one of the important results of their decomposi- 

 tion. 



Animal membranes and oil decompose, and pass off for the most part as gases. Por- 

 tions of the carbon and hydrogen often remain in the bed in which they are buried, 

 giving it a dark color, or making sometimes mineral oil or coal. Impressions of the 

 soft parts of animals, as of some Cephalopods, and the membranous part of the wings 

 of Pterodactyls, have been found in rocks; but they are very rare. 



The tissues that penetrate shells and bones are sometimes in part retained by the an- 

 cient fossil. Two cases are mentioned by Barrande, of the conversion of the animal 

 material, within a Lower Silurian Orthoceras, into adipocere (an animal substance 

 having the appearance of spermaceti); and he speaks of them as the oldest mummies 

 ever exhumed. 



A small percentage of phosphates and fluorids is derived from decomposing animal 

 tissues. 



