BOSTON MOUNTAIN PHYSIOGRAPHY 1605 
it certain that there must be no general beveling of hard and soft 
layers. Professor Purdue says: 
Structurally, in the western part of Arkansas, these mountains are a broad 
flat anticline, the strike of which is east and west. According to the geologists 
of the Arkansas Geological Survey, it appears that the extreme eastern part 
of the region is monoclinal in structure with the dip to the south. 
The dissected plain is also slightly tilted and slightly bowed, 
but I invite someone to show that it is strictly parallel to the 
structure. Specific data on this point are wanting. I believe 
that the plain actually bevels the slightly inclined strata, and if 
the summit-plane of the outliers on the north be admitted into 
the argument, I know that it does. (6) By elimination, the pene- 
plain hypothesis comes to the front as that which furnishes the 
most natural explanation of the phenomena observed and violates 
no established principles of physiography. I believe the pene- 
plain character of Boston Mountain is as firmly established as 
that of any other recognized dissected peneplain in eastern 
America. It is not proved and perhaps never will be as proof 
is made in other departments of science. A strong suspicion 
now existing that an ancient peneplain is represented may be 
strengthened as more precise data are recorded and in time the 
critics may cease opposition. At present their activity is desir- 
able as stimulating the collection of evidence. 
As precedents for disregarding, in the conclusion that the 
dissected plain at the summit of Boston Mountain has an age 
greater than that of the ‘main Tertiary” peneplain, the argu- 
ment drawn by Professor Purdue from the contrast in stage of 
maturity of drainage and topography on the two areas, I will 
mention the plateau of West Virginia with its narrow valleys, 
standing as a residual on a Tertiary baselevel which in other 
portions of the Appalachian region has broad basins and mature 
topography; and the Niagara plateau of northeastern Iowa, ris- 
ing prominently above a lower dissected plain whose valleys are 
equally as large. 
Oscar H. HERSHEY. 
BERKELEY, CAL., 
Jan. 21, 1902. 
