164 OSCAR H. HERSHEY 
phenomena as meandering stream courses and monadnocks are 
valuable adjuncts, but not essentials. How do these principles 
apply to the Boston Mountain region? 
In arriving at the most natural explanation of the uniformity 
in height of the Boston ridges, six hypotheses may be briefly 
examined: (1) That it is a plain of aggradation of Upper Car- 
boniferous age which remained intact until very late geologic 
time because of having stood virtually at sea level. This is call- 
ing into play a possibility which is not a probability. From what 
is known of the history of the continent in post-Carboniferous 
time, it may be considered unnatural. However, even allowing 
that such a strange coincidence may have occurred, I should 
still claim the summit plane of Boston Mountain as representing 
a baselevel of subaerial erosion, an appendage to a true pene- 
plain. (2) That it was planed off by marine erosion and a thin 
sheet of Cretaceous or Tertiary sediments deposited on it. A 
submarine shelf, twenty miles in width, would have a consider- 
able thickness of sediment resting on its seaward portion, and 
some remnants should remain on the flat-topped hills. If the sub- 
mergence was very short, I should claim the reduction of the 
area to a plain condition to have been virtually the work of sub- 
aerial denudation, very slightly aided by marine action. Asa 
matter of fact, there is no collateral evidence of such submer- 
gence in post-Carboniferous time and the drainage system is 
against it. (3) That the uniformity in height of the sepa- 
rate ridges which together constitute the Boston Mountain can 
be attributed to the intersection of the slopes of valleys having 
a common baselevel isan untenable position because most of the 
ridges have truncated summits. (4) The conditions of the soil, 
climate and amplitude of elevations are not such as to give value 
to any argument based on differential protection by vegetation. 
(5) Thatit is a structural plain resulting from the unequal resis- 
tant properties of the Carboniferous strata eroded. This implies 
that there be strict parallelism between the plain and the bedding 
of the rocks, for studies in the western states where this agency 
has had full play in the production of topographic forms, make 
