ORIGIN OF THE OOLITES 597 



in the shale can be a source. Very evidently it is not the quartz, for the 

 quartz grains in the shale are sharply angular, showing no evidence of 

 solution. The only other constituent is kaolin, and it is unlikely that any 

 solutions in the shale would attack this extremely resistant mineral. No 

 other silicates could be recognized in the shale. There is no more likely 

 source from the outside, as the adjacent beds also are sandstones and 

 shales. Suitable solvents for silica are extremely rare among ground 

 waters, yet one must be sought if the oolites originated by replacement. 

 The view that organic acids are adequate solvents has fallen into disfavor 

 in recent years. 



The conclusion is reached that siliceous oolites in shale do not owe their 

 origin to the replacement of calcareous oolites. 



Source of the Silica 



It is believed that the oolites are due to the precipitation of colloidal 

 silica, which was brought by the streams into the sea or inclosed body of 

 water. The streams which flowed into this body of water drained from 

 an unknown area to the w^st. The character of the rocks of this drainage 

 area is, of course, unknown, but some part of the material in solution, at 

 least, may have been derived from any exposed Lower Paleozoic forma- 

 tions. Possibly the larger portion of the drainage area consisted of Prc- 

 cambrian and igneous rocks. It would appear that the character of these 

 stream waters would be comparable to those of the streams that are drain- 

 ing areas of mixed types of rocks today. Many analyses of the waters of 

 such streams are available, and these afford data to test the adequacy of 

 the idea that the streams may be a source of silica. 



There is only one analysis of the water of the streams in this region, 

 and that is of the waters of the Popo Agie, which drains mainly a granitic 

 area, but crosses Paleozoic sediments in its lower course. Slosson's^ analy- 

 sis shows that approximately 8 per cent of the material in solution is 

 silica. Ileadden^*^ gives an analysis of the Arkansas Eiver at Canon City, 

 Colorado, which shows 8.19 per cent silica, while another stream, the 

 Poudre Eiver, in northern Colorado, after flowing for fifty miles over 

 granitic rocks, contains 23.5 per cent silica. It will be necessary for our 

 purpose to give only some averages of a number of streams in various parts 

 of the United States. Dole^^ gives analyses of the principal streams of 



OE. E. Slosson: Bull. Wyoming Agri. Exp. Sta., No. 24, 1805, p. 119. 

 10 W. P. Ileadden : Bull. Colorado Agri. Exp. Sta., No. 82, 1903. 



" R. B. Dole: Tho quality of surface walors in the United States. Water Supply 

 Paper No. 236. 



