92 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
stratified series, aggregating about 15,000 feet within the limits of 
the model, suggests a long continued period of depression and 
deposition, so often encountered when the ancient history of the 
earth is deciphered. 
Uplift from this period of depression and deposition was unequal, 
being greater in the northeast than in the west and southwest; thus 
the tilted attitude of the strata was produced. The former greater 
extension of the stratified series eastward over the crystallines may 
be inferred from the manifest truncation of the strata to-day. A 
great part of the denudation by which the present form has been pro¬ 
duced must be referred to a c}^cle previous to that in which the 
existing valleys have been carved; for in this way the general sky¬ 
line of the region can be explained best, as it obliquely bevels across 
the older and younger rocks. A rough peneplain, RS, may have 
then been carved, making a distinct angle with the peneplain of 
much earlier date, KN; the earlier peneplain being buried in the 
west, KL, and worn away in the east, MN ; a part of it, LM, 
being stripped and made visible where the crystalline rocks run 
under the stratified series. Like many another fossil, this ancient 
land surface has been preserved by burial and is now revealed by 
weathering. As in many another case the weathering has injured 
the fossil while revealing it, for it is less perfect now than when 
it was buried. 
The later peneplain, RS, is now uplifted in the north and 
depressed in the south, where the land runs under the present sea. 
In this attitude it has been stronglv dissected with reference to the 
existing baselevel, BY; thus the valleys and shore line of to-day 
have been carved. 
