674 KANSAS CITY REVIEW OF SCIENCE. 



loo parts of alumina there were 347.5 parts of silica before decomposition, the 

 proportion in the resulting clay is only 100 : 11 8. 3. 



When we consider the vast amount of silica that has thus been carried to the 

 sea, we are forced to conclude that it must have been deposited by some other 

 means than that of life. The amount is too great to be referred to so small a- 

 number of microscopic organisms. Even if we did not have the positive evi- 

 dence in the crystallized grains of sandstone, we could draw such a conclusion ;. 

 but when we have this we may reasonably conclude that other portions have also 

 been deposited without such assistance. The question then arises, what is there to- 

 indicate that the greater part of the silica in the petrified remains of organisms is- 

 derived from animals and plants that secrete siliceous matter ? In all cases where 

 true petrifaction has taken place the silica must have been in solution, and if the 

 spicules of Sponges, etc., are once dissolved, the silica simply takes its place with 

 other portions that are held in solution and can no longer be looked upon as of 

 organic origin. The extraordinary occurrence of chert beds in the sub-carbonif- 

 erous may be due to the fact that it succeeded an age when the conditions were 

 most favorable for the rapid decomposition of ancient crystalline rocks. The air 

 was probably much richer in carbonic oxide than at present, and there was a larger 

 surface of metamorphic and crystalline rocks exposed than has been at any sub- 

 sequent time; because, as the decomposition continued, portions of the surface 

 once exposed would be protected from the atmosphere by the clays and soils- 

 formed, and the new formations that subsequently emerged contain but few 

 rocks that would yield silica by the action of decomposing agents. There was 

 the great V-shaped ridge on the north which extended as far south as Pennsylva- 

 nia and also included a large portion of Ohio. A ridge extended down the Alle- 

 ghenies as far as South Carolina. There was also a large tract in Mis.souri,. 

 including the greater portion of the Ozark Mountains. The great central basin. 

 of the Mississippi Valley was thus almost entirely surrounded by hills of decom- 

 posing rocks, the silica of which was being poured into its waters. Everything 

 was thus favorable for a maximum formation of siliceous strata. If the decompo- 

 sition of these ancient rocks was as rapid as we have reason to suspect, the 

 proportion of silica which the ocean waters contained was much greater than at 

 the present time. Graham* has shown that when pure silica is held in solution, 

 1 ooQ -Q part of an alkali or alkali earth carbonate precipitates it. At the present 

 time the greater portion of silica is held in solution by an alkali that is an alkaline 

 silicate. But this is not necessarily so. In the article above referred to, Ebel- 

 man has shown that an alkali is not essential. The following are his words ; 

 " The researches which I have described have shown that the silicates without 

 alkalies are decomposed as easily as the feldspathic species, sometimes even 

 before them, and that the removal of the silica is, in certain cases, more complete 

 than from [in] kaoline. The separation of sihca may, therefore, be entirely 

 independent of alkalies." 



♦ Philosophical Magazine (4). Vol. 23, p. 296. 



