600 ^y. a. taer — oolites ix shale axd their origin 



distribution of the silica in the watei% (b) in the salinity of the water, 

 and (c) in the rate of accnmnlation of mud and sand. That the large 

 oolites are merely the resnlt of growth of the small ones is shown by the 

 central zones of the larger ones being the same size as the smaller oolites. 

 The outer surfaces of the oolites are rough, because the oolites were buried 

 so fast that they could not be smoothed by current or wave action. 



COXCLUSIOX 



The oolites in the shale constituting the Popo Agie beds are believed 

 to be due to the direct precipitation of colloidal silica introduced into the 

 saline, shallow waters by the streams flowing from the adjacent land areas. 

 Proof of their original character is the uniform distribution of the oolites 

 through the sliale, tlie distribution of sand grains througJi the oolites and 

 the matrix, all lack of growth effects in the oolites, the interference of 

 the oolites (never seen in calcareous oolites), the slight compression of 

 the shale and flattening of the oolites, and the precipitation of the oolites 

 in shallow, agitated water. 



The precipitation of the silica was proljably due to the electrolytic and 

 saline character of the water, the resulting siliceous gel aggregating into 

 the oolites, which were buried as the silts and sands accumulated. 



