8^ Expedition to the 



The precipices tn both varieties, are often lofty and per- 

 pendicular, but the projections and anglt-s of the red are 

 taiore worn and rounded than those of the gray. The narrow 

 defiles and ravines, which the streams of water have exca- 

 vated, are less tortuous, when they are entirely in the gray 

 sandstone, than in other instances. The springs of water 

 flowing from it, are more free of mineral impregnations than 

 such as are found in the other variety. It sometimes consists 

 of glittering crystalline particles, but does not in this case ap- 

 pear to be a chemical deposite. In fine it appears under an end- 

 less variety of characters, of which it would be in vain to at- 

 tempt the enumeration. Although the gray sandstone, is not 

 invariably distinguished by the presence of an argillaceous 

 ingredient, yet it is constantly found in connection with the 

 soft clay slate, or bituminous shale and coal wherever these 

 are met with. Gypsum and muriate of soda are as common- 

 ly found in- or near the red variety. 



These sandstones being entirely mechanical aggregates, 

 consisting of rounded fragments of rocks, formerly constitu- 

 ting a part of the primitive mountains, would seem to have 

 been deposited at a very remote period, when the waters of 

 the primeval ocean covered the level of the great plain, and 

 the lower regions of the granitic mountains. 



Subsequent to the deposition of the horizontally stratified 

 rocks, the position of these, in relation to the primitive, has 

 been somewhat changed, either by the action of some force 

 beneath the primitive rocks, forcing them up to a greater 

 elevation than they formerly possessed, or by the sinking 

 down ot the secondary, produced by the operation of some 

 cause equally unknown. Without supposing some change of 

 this kind, can we account for the great inclination of the 

 margin of the sandstone rock, which is found resting against 

 the granite almost perpendicularly? Nearly contemporane- 

 ous to this change, was the retiring of the sea, and the con- 

 solidation of the trap rocks. The beds of loose sand and gra- 

 vel, which are still accumulating, have been formed in part, 

 from the disintegration of the sandstones, and conglomerates, 

 partly by the action of those currents of water, which are 

 constant!) bringing down small fragments from the primitive 

 rocks, and depositing them in the plains. 



The absence of any formation of limestone, is a distin- 

 guishing characteristic of the country under consideration. A 

 traveller to the upper part of the Missouri mentions, *' cal- 

 careous and petrosiliceous" hills, as existing in the coal dis- 



