206 REMARKS ON SANDSTONE AND 



formation of secondary which we are now consideringc. We 

 have already mentioned that in an horizontal position it co- 

 vers a very extensive tract to tlie south west of tlie Arkan- 

 saw, that it skirts the eastern side of tiie Kocky Mountains, 

 rising at a great angle from beneath the superimposed strata. 

 It also occurs in the Catskill Mountains, and in the Suit Dis- 

 trict in the western part of the State of New York, having a 

 similar relation to the secondary rocks in that quarter. The 

 old red sandstone of Werner has hy some been referred to 

 the rocks of transition, and considered as tlie most recent 

 member of that class ; others have considcM-ed it as the old- 

 est of the secondary. But it seems to have happened here, 

 as in other parts of this yet imperfect science, that distinc- 

 tions have been made, for which there is really no founda- 

 tion in nature. The red sandrock now under consideration 

 appears at one place with every character requisite to place 

 it among the rocks of transition, at another it is manifestly 

 secondary ; yet its continuity may be traced through minute 

 shades of gradation, or by a sudden transition from one of 

 these points to the other. 



Immediately above the red sandstone, when any rock rests 

 upon it, I have commonly found a greyish or yellowish white 

 sandstone which may perhaps be with some propriety dis- 

 tinguished as the second variety. It commonly contains a 

 greater or less proportion of clay in the cement, and has a 

 somewhat slaty structure. Hence it may properly be call- 

 ed argillaceous sandstone, though in some respects it may 

 differ from the rock known to many by that name. 



2. Argillaceous sandstone. This variety being uppermost 

 in actual position, is perhaps more frequently seen on the 

 surface than the other; while at the same time it is |)robal>ly 

 less al)undant. The line of separation betwixt the two 

 is often manifest and well defined, and in other instances 

 they pass by imperceptible gradations into each other The 

 upper or argillaceous sandstone is usually more comp:ict 

 and more homogeneous in its composition than the red. It 

 is also of a close texture and a fine grain, embracing few 



