508 REMAliKS ON SANDSTONE AND 



the position it occupied relative to the immense masses ot 

 flcetz limestone and other secondary rocks which are now 

 found in that valley. 



But as the red variety is still extensively disseminated, 

 and usually accompanied by those valuable substances, salt 

 and plaister, (sulphate of lime) it may not be amiss to trace, 

 as far as our examinations have enabled us to do it, the out- 

 line of the region it occupies. 



As we have before mentioned, it is found in the vicinity of 

 the river Platte, in a highly inclined position, coverins; a nar- 

 row margin, immediately at the foot of tlie Rocky Mountains. 

 From the account of Lewis and Clarke, we are disposed to 

 believe that it exists under similar circumstances near the 

 falls of the Missouri. On the Canadian, it is constantly met 

 with from the sources of that river, which are on the bor- 

 ders of New Mexico in west longitude about 106 degrees, 

 nearly to its confluence with the Arkansaw, in 97 degrees. 

 The waters of the Canadian, from flowing over the sandstone 

 in question, acquire an intense red colour, and are so im- 

 pregnated with muriate of soda and other soluI>le salts, as to 

 be unfit for the uses to which common water is applied. 

 This, it is well known, is also the case with the waters of 

 the three small rivers tributary to the Arkansaw, above the 

 Canadian, on the same side also with the waters of Red 

 River. Hence the conclusion appears to be justified, that 

 this rock extends from near the Arkansaw on the north to 

 a point beyond Red River on the south, and from near the 

 mouth of the Canadian an unknown distance to the west be- 

 yond the remotest sources of that river. It is not unlikely 

 that it exists about the sources and upper branches of the 

 Rio Colorado of California, though we must acknowledge 

 that the name of that river is the only foundation we are 

 acquainted with for sucli an opinion. 



Near the mountains at the head of the Platte, and for a 

 great distance to the south and east of the higli peak, the red 

 sandrock is covered by the stratum of argillaceous sand- 

 stone already mentioned. It has, however, in many in- 



