962 The Materials of the Appalachians. 
this must be left for further investigation. My purpose in this 
paper has been to show that the sandstone beds of Middle and 
Western Pennsylvania imply the past existence of quartz-rocks — 
more extensive by far than their present remains would indicate, 
and that the white pebbles of these Conglomerates imply an im- 
mense extension of the ledges of milky quartz that are now to be 
seen in the rocks of the South Mountains. ; 
-In the map and section accompanying this paper an attemptis 
made to represent to the eye the leading facts in the argument. 7 
It is of course quite impossible to draw the latter to scale, nor 
would any useful purpose be served by the attempt. The ut- 
colored portions show the soft beds lying between the sandstones, 
which are really in most cases thicker than the sandstones them — 
selves. The only points which the section is intended to bring _ 
out are the profound Appalachian trough in which the palæozoic 
sediments were deposited, the westward thinning of all, both sand- 
stones and shales, and the fining of the Conglomerates in he 
same direction. i 
Aei rrr S YL VAR OM 
NT ak,” ae PS ae ta eae er Tn RN wie Be 
° Ta EG 
Lagrammatic Section of Pennsylvania 
Fom East to West. 
a Ardina a Oriskany c atskilt -pocons 
(To be concluded.) 
