SILICEOUS OOLITES IN PENNSYLVANIA 269 
and one which has doubtless been very active in this area since it 
emerged from the sea. In the bulletin, The Data of Geochemistry, 
F. W. Clarke has presented evidence of the great influence of organic 
acids in the solution of silica.t A. A. Julien, T. Sterry Hunt, and 
many others have made important observations and experiments 
on the solvent action of these acids, and since there is reason to 
Fic. 7.—Photomicrograph of odlites, illustrating the solution and granulation of 
the sand grains forming the nucleus of the concretions. XX 45. ; 
believe that these agents have been at work for extended periods 
of time and the solution and transportation of iron and silica are 
known to be going on at the present time under their influence, it 
seems reasonable to conclude that organic acids may be regarded 
as the most important agent in the formation of these siliceous 
oolites. 
t Data of Geochemistry, Bulletin 330, U.S.G.S., p. 84. 
