a a a 
x Ge 
s 1887] The Materials of the Appalachians, 1057 
_ quartz-bed of the whole series was laid down, - Judging by its 
effects this was the most extensive disturbance of the four. It 
formed a bed of sandstone reaching in some places a thickness 
of seven thousand feet, for the Catskill and the Pocono united 
sometimes surpass even these enormous figures, This implies . 
immense erosion elsewhere, and the inference seems quite just 
that this Catskill-Pocono Ridge formed a conspicuous or an en- 
_ during feature in the Upper Devonian landscape. 
_ But it disappeared and a time of inaction followed, marked by 
the deposition of numerous soft beds on the eastern sea-board 
din the midland basin. These are now the Lower Carbon- 
irous Rocks. Again the compressing force overcame its resist- 
ace and a fourth ridge arose, whose destruction in due course 
é furnished the material of the Pottsville Conglomerate, underlying 
the Coal-Measures. The manufacture of quartz-sand and of peb- 
_ bles again began, and a sheet of this material was spread over 
: Western Pennsylvania, West Virginia, and Ohio, gradually di- 
-Minishing in thickness and in size as it recedes from the parent 
g On this, when the stock of quartz was exhausted, were 
: kid down the coal-beds, with all their intermediate limestones, 
Sales, and sandstones, 
Such, as I read it, was the history in brief of these four sand- 
€s. I have omitted all details, all minor beds, and have 
: touched only the great features of the story. Four acts in the 
: aa a are now complete, and the fifth and last follows in due 
Course, 
; 
ai 
E 
be No trace remains of the four elevations above mentioned ex- 
a four monumental sandstones built up from their remains. 
eg case is different with the last. This was the great earth- 
wet that occurred at the close of the Carboniferous period. 
= the suspended force again came into action, and the newly- 
med coal-beds were crushed and crumpled into the arches and 
è i in which their remains now lie. Of this latest catastrophe 
“dant traces remain. The ridges then formed have not yet 
‘appeared, and all the ranges of Pennsylvania, with the possi- 
that ception of the South Mountains, date their beginning to 
in kira This last act in the drama is one of the great Er 
fhe tican geology. It is the greatest epoch in the history ° 
È “ontinent., The Appalachian Revolution closed the Palaeozoic 
and lifted North America above the waves of the ancient ap 
a 
