21S REMARKS ON SANDSTONE AND 



following the direction of what were formerly the beds of 

 small brooks. This appearance was in one instance so strik- 

 ing, that several of the party who saw it were induced to be- 

 lieve that the materials whicli constituted the ridge had for- 

 merlv been ejected in a fluid state from beneath the surface. 

 We had not an opportunity to examine the surrounding coun- 

 try with sufficient minuteness to enable us to form a conjec- 

 ture concerning the accuracy of this opinion. Some high 

 and sharp conic hills were visible to the westward, but at a 

 great distance. Two of this kind, which stand near each 

 other and appear to be detached from the primitive moun- 

 tain, are called the Spanish Peaks, and at the end of July, 

 snow was still to be seen on them. 



Where either of the two rocks last mentioned occur, it is 

 not uncommon to meet with detached masses of a substance 

 greatly lesembling the pumice stone, which is an article of 

 commerce, and entirely similar to that which is often seen 

 floating down the Missouri. It is usually of a faint red or 

 dirty yellow colour, but sometimes brown or neaily black. 

 It feels less harsh than common pumice stone, and is com- 

 posed almost wholly of clay. 



With regard to the alluvial formations of the portion of 

 country of which we have been speaking, little need be said. 

 The trap rocks are often covered with a scanty daik co- 

 loured soil, free from pebbles or waterworn masses, and of 

 consideralile fertility. 



The sandstone districts are often covered to a great depth 

 with rounded fragments and particles of rocks similar to 

 those of the primitive mountains. The fineness of this soil 

 bears a pretty constant proportion to tlie distance from the 

 mountain at which it is examined. On the lower part of the 

 Platte scarce a stone or a pebble is to be seen. At a dis- 

 tance of two hundred miles from the mountain the surface 

 is often like a gravelled walk or a street paved with pebl)les, 

 and near the foot of the mountain it is covered witli large 

 boulders. The soil is almost invariably arid and barren. 

 The total absence of any formation of limestone in the dis- 



