1058 The Materials of the Appalachians. [Dec. : 
We need, therefore, only extend backward a known process to 
explain the origin of these four sandstones. We can in imagina- 
tion see a series of ridges rising one beyond another in time gone 
_ by on what is now Eastern Pennsylvania. We see these ridges 
destroyed as, or after, they arose, and we see their wreckage 
forming new strata at a lower level. Extinct mountains, we may 
call them, which have passed away and left no trace on the face 
of the earth save the four great sandstones which form their 
monuments, 
The wide plains of Eastern Pennsylvania were the standing- 
ground of these ridges. An extension of the quartzy strata of 
the South Mountains over this district where the mica-schists of 
the Archzan are now exposed, the successive crumpling of these | 
strata and their subsequent erosion, complete the picture. Aba 
dant material was obtainable, for we must be careful not to limit 
the area to its present size. Crumpling causes compression, and 
the site of Philadelphia must have then been much farther from 
that of Harrisburg than it now is.* The Archæan terranes east 
of the South Mountains were then deeply buried beneath later 
deposits since removed. Each successive area of crumpling me ; 
east to west became compressed beyond all further compression q 
and then added itself to the compressor, thus aiding to shove 
forward the adjoining area just as layer after layer of pul : 
added in front of a snow-plough until the resistance beme i 
great enough to stop the engine. 
See EET Ne tee 
ologist is often 
distribute this 
m the ridge a 
the county 
remarkable a 
the quary 
In the consideration of this subject the ge 
puzzled to find a transporting force sufficient to 
sand and these pebbles over so great an area. Fro 
whence they were derived they have been strewn over 
to the westward for five hundred miles, in sheets of 
evenness, gradually thinning out as the distance from © 
increases. The Oriskany is especially remarkable in anes of 
It extends over the whole area above named, and ove" ss of 
New York, Maryland, and West Virginia, forming r d 
almost unbroken continuity, but seldom exceeding two a ; 
or three hundred feet in thickness. To what powt i 
attribute the formation of so thin and yet so broad a ie 
Without dogmatizing on this difficult subject, there hee 
*See American Naturalist for March, 1885- | 
ha 
