1887] ` The Materials of the Appalachians. 957 
-Harrisburg would be greater by many miles. The present Key- 
_ stone State bears to the original palæozoic Pennsylvania some- 
_ What the relation which the skin of a shrivelled apple or potato 
_ bears to the same skin when plump and fresh. But of this no 
4 account is taken in the estimate given above. 
_ Turning now to the consideration of the land from which all 
_ this sediment was derived, we find that only about one-tenth 
4 part of the State can have been above water in palzozoic days, 
_ and that this small portion lay in the southeastern corner. 
 Allthe rest is covered with palzozoic rocks. This means that 
_ the only visible source of the material of which these rocks are 
_ composed and which we have found is a mass of at least thirty-six 
> thousand square miles in surface and three miles thick, is an area 
p” Pennsylvania of four thousand square miles. Restore in 
F magination these massive sheets of rock to their original source, 
E and it will be necessary to pile the material twenty-seven miles 
‘ high on the palzeozoic land of the State in order to obtain a 
J sufficient supply, —in order to build a quarry from which the 
_ fers and sea-waves of that age could cut out the blocks which, 
-When torn up and scattered, have composed the palæozoic rocks 
4 of Pennsylvania, Pr K 
Q A correction may be made in the above figures on account of 
De Probability that some of these sediments came from New 
= sey on the northeast and Maryland on the south. Parts of 
q = these States consist of archæan terranes now exposed and 
4 hoa now covered with later mesozoic red sandstones. But 
4 the areas in both States are added to the possible archean 
4 hg of Pennsylvania, they will not more than double it, and 
f . shall still be compelled to assign an enormous depth (thirteen 
4 miles) to the eroded ancient land before sufficient material is at 
a to form th 
ace here available. Among these heavy deposits 
oe Some thin and local beds, four great sandstones, 
sa less pebbly. They are as follows in descending 
The Pottsville Conglomerate, Carboniferous. 
