'2'>\2 The American Geologist. October, 1894 
seat of the existing dicotyledons, then by the lowering of the 
surface by gradual consumption of the interstream areas, 
these forms must have been brought into conflict with the an- 
cient flora of the lowlands and thereby forced into a contest 
for supremacy. The uplands which still remained in the form 
of monadnocks rising above the base-leveled plain served as 
reservoirs for replenishing any weakening in the cohorts of 
the endogenous species. 
We should expect to find the influence of baseleveling dis- 
advantageous to the upland flora and hence favorable to the 
continuation of the old Paleozoic types. The fact that the 
endogens prevailed in spite of this geographic change would 
make it seem that the upland mainly endogenous forms were 
hardier and accommodated themselves to the lowlands, ex- 
cluding the older flora. Thus, at the base of the Upper Creta- 
ceous on the east coast of North America, we find the dicoty- 
ledonous forms at or near sea-level in the Raritan group in the 
period following the baseleveling of the Piedmont plateau. 
Recapitulation. 
To sum up the faunal history of the Mesozoic alone, we 
have seen that pari passu with the creation of broad lowlands 
there was brought on to the stage a remarkable production of 
reptiles, a characteristic lowland life; and we note that the 
humble mammalia were excluded from the peneplain or held 
back in their development, so far as we know them by actual 
remains, during this condition of affairs until the very high- 
est Cretaceous. At the close of the Mesozoic, the area of the 
peneplain was uplifted and there came into it the new life. 
Not only the changed geographic conditions, but the better 
fitted mammalia also were probably factors in exterminating 
the life of the peneplain. It would be more satisfactory if we 
could go farther in the correlation than to point out the bare 
correspondences in organic and geographic development 
which seem to be related so closely in time. In tracing these 
related changes attention has necessarily been called away 
from other perhaps equally cogent means of dispersing and 
modifying life. There were numerous changes of level and 
climate which tended to qualify and perhaps locally to nullify 
the effect of the peculiar geographic conditions of the Middle 
Mesozoic; but after admitting all these, it still seems fair to 
