366 THE GEOLOGICAL HISTORY" OF THE 



of some iron-containing mineral, now decomposed and in part 

 removed. Soft slate-colored specks and pieces, which are doubt- 

 less fragments of the slate formation beneath, are also present. 

 The cementing matter of the rock is a light grey powdery 

 substance, probably decomposed feldspar, which appears to be 

 quite easily removed by the mechanical action of rain. There 

 is no effervescence with acids, showing the absence of carbonates. 

 Because of its constituent minerals the rock is light grey in 

 color, although the joint surfaces are frequently stained a dark 

 red by iron oxide. This is a further indication of removal of 

 iron oxide ; and the absence of carbon from these coarse and 

 somewhat porous sandstones when compared with its abundance 

 in the accompanying fine-grained argillaceous beds, is suggestive 

 of the mutual decomposition of the organic substances and iron- 

 containing minerals, and their subsequent removal in solution by 

 the underground water. 



The prevalent red color of the overlying Triassic red sand- 

 stones, which, without doubt, were derived in large part from 

 these older sandstones, is probably due to the subsequent oxida- 

 tion and precipitation of these same dissolved iron compounds. 



Because of their relations to adjacent formations, and their 

 fossil contents, this series of beds has been regarded as of Lower 

 Carboniferous and even of Devonian age.* 



A short distance south of the last outcrop of sandstone, 

 greenish-grey compact slates with clean-cut joint planes come 

 to the surface in many places along the summit of the ridge, 

 and generally underlie the country to the south and west. At 

 this locality the cleavage is nearly vertical and the beds 

 dip northwesterly at angles of from 20 to 70 degrees. Several 

 almost vertical veins of quartz, from one to two feet in thickness, 

 lie in the slate along the southern brow of the ridge approxi- 

 mately parallel with the cleavage planes of the rock. 



Just below the southern brow, a narrow band of sandstone, 

 exactly similar to the coarser beds of Carboniferous sandstone 

 above described, crops out at the top of the slope. Its elevation 



*See H. M. Ami, Summary Report of the Geol. Surv. Dept. for 1898. Pp. 180-182. 



