956 © The Materials of the Appalachians, Do, 
It is further admitted, at least, I think, by all Pennsylvania 
geologists, that this ancient land, whose destruction supplied 
the materials for these immense deposits, existed to the east and 
southeast of the Appalachian region. It is sufficient to mention 
the increasing thickness of the strata towards the southeast and 
the greater coarseness of their material in the same direction, to 
convince almost every one that the palzeozoic land must be sought 
there. 
Having laid down these premises, I propose first to notice the 
immense mass of the Appalachian deposit. 
- Pennsylvania contains at present about forty thousand square _ 
miles of surface. Of this about nine-tenths are covered with the 
palæozoic rocks; that is, about thirty-six thousand square miles. 
Since their elevation above water erosion has destroyed vast 
quantities, but, as said above, there is positive evidence that when 
they lay in horizontal sheets beneath the ancient ocean they 
measured from eight miles at the east to three miles at the west 
in depth. It cannot, therefore, be excessive to assume peer 
If this be 
erm measurement as an average over the whole area. 
done, we find the palzeozoic deposits of Pennsylvania represe! 
bya mass three miles thick and thirty-six thousand square TA 
in area. y 
This estimate is far below the truth for the following rc 
1. As mentioned above, nearly the minimum thickness ae : 
loyed over th 4 
ploy the whole area. cP ems 
$ 
2. Vast quantities of material now lying outside 0 
vania, in Ohio and Western New York, are omitted. 
3. The corrugation and consequent contraction of the surface 
during the formation of the Appalachian earth 
garded, sf 
The importance of this last fact must not be overlooked: 
paper by the author, read before the British Association at 
treal in 1884, and printed in the AMERICAN Na ei 
March, 1885, the great diminution of surface which the : 
in question underwent during the process of crum the 
pointed out. Palzozoic Pennsylvania was far larger than ie 
isting State. Could the strata be flattened out 
folds are dist 
laundry—her anticlines and synclines thousands of aoe 
would be added to her size, The distance from $ 
