; 1887] The Materials of the Appalachians. ~ 1055 
Feet, 
Shale and limestone (Devonian) 4000 
2 Sandstone and pebbles (Oriskany Sandstone) 300 
Shale and limestone (Lower Helderberg, etc.) 300 
` I Sandstone and pebbles (Medina, Oneida, etc.) 1500 
Shale and limestone (Trenton, etc.) 5000 
Sandstone (Potsdam), 400 
Here are four vast beds of sandstone, all more or less con- 
 glomeratic, lying between thick masses of softer rocks. In as- 
ending order they are the Medina, the Oriskany, the Catskill- 
Pocono, and the Pottsville. They vary in hardness, in thickness, 
‘din coarseness, but they all agree in being composed of almost 
nothing but quartz in the form of pebbles and of sand. 
Now, we are quite safe at the outset in asserting that these 
bur great sandstones, with their alternating shales, represent as 
any changes in the conditions of deposition. The geographical 
Mangement of land and water that allowed the deposition of 
Sale would prevent that of sandstone. Results so different 
“gue different causes. Regarding the origin of the shales I do 
‘ Mt now propose to inquire, and will therefore dismiss them with- 
t further notice, and refer only to the four great sandstones 
dready mentioned. 
Itis obvious that each of these implies the destruction of an 
al amount of rock elsewhere. They were not made from 
; Inch by inch and pound by pound they and their 
Pebbles represent and measure the rock whence they were hewn. 
So vast an accumulation of quartz, therefore, implies an equally 
quarry from which it was obtained. But no such quarry 
“sts; it has entirely disappeared. 
y 
WED 
“use, I think we may see in them a history of what was 
ng elsewhere during their formation. ak 
“re, then, shall we seek the Eastern quarry of quartz 
ae the massive Medina Sandstone was derived? j 
