A. L. Ewing—EKrosion of Limestone. 29 
water into the southern hemisphere sufficient to produce true 
glaciation on the opposite hemisphere. That the geographical 
conditions obtaining on the southern hemisphere during Ter- 
tiary times were probably of such a character is an opinion 
advanced by Mr. Wallace himself. ‘There are,” he says, 
“many peculiarities in the distribution of plants and of some 
groups of animals in the southern hemisphere, which render it 
almost certain that there has sometimes been a greater exten- 
sion of the antarctic lands during Tertiary times; and it is 
therefore not improbable that a more or less glaciated condition _ 
may have been a long-persistent feature of the southern hemis-. - 
phere, due to the peculiar distribution of land and sea, which 
favors the production of ice-fields and glaciers.” (p. 192.) 
[To be continued. ] 
Art. VII.—An atiempt to determine the Amount and Rate of 
Chemical Erosion taking place in the Limestone (Ca/ciferous 
to Trenton) Valley of Center County, Pa., and hence applicable to 
similar regions throughout the Appulachian Regions; by A. L. 
__In the following, the nature of the problem precludes the 
idea of even a close approximation to accuracy. It is claimed 
however that these determinations form a more reliable basis - 
than mere estimates. 
The method pursued is as follows: The amount of water 
flowing from a given hydrographic basin in the region under 
question is determined from the cross-section and velocity of 
the stream draining it. The amount of solids in the water is 
determined by evaporation; these data with the area of the 
asin form the basis of calculation. 
The region selected is that of the Spring Creek basin which 
forms a considerable portion of the limestone valley of Cen- 
ter County. The measurements were made above the old dam 
below Bellefonte and below the entrance of all visible triba- 
taries from the valley. : 
hat a fair conception of the region may be had a brief 
explanation of its geology i 
would form an immense mountain-like plateau over 20, 
feet above its present height. As it is, the floor of the valley 
