Baseleveling and Organic Evolution. — Woodworth. 209 
THE RELATION BETWEEN BASELEVELING AND 
ORGANIC EVOLUTION.* 
By. J. B. Woodworth, Cambridge. Mass. 
CONTENTS. 
Page. 
Introduction 20H 
Synopsis 210 
Parti. Historical Sketch 210 
Views of the British School 211 
Views of the American School 213 
Part II. General Effect of River Changes on Fluvial Faunas 214 
Through headwater diversion ; 215 
Through antecedent streams 2ir» 
Through alluviation 216 
Through slight submergence 218 
Through elevation and revival of streams 216 
Effect of baseleveling of a mountainous region 217 
Fading away of divides 218 
Degradation of uplands 219 
Spread of lowland conditions 220 
The peneplain an open field for land life 220 
Uplift and dissection of the peneplain 221 
Part III. The Jura-Cretaceous Peneplain 221 
Non-marine beds rest on the peneplain on the Atlantic coast 222 
Post-Cretaceous history of the peneplain 22:1 
The coast shelf the correlative of the peneplain 223 
The life inhabiting the peneplain 224 
Freshwater mollusca 224 
Fishes and amphibians 225 
Reptiles correlated in development with the growth of the peneplain 226 
Objections arising from extent of peneplain 226 
Objections arising from distribution of reptiles 228 
Mammalia unfavorably affected by the peneplain ami reptiles 228 
Dinosaurs and peneplain disappear at close of Mesozuic 229 
The Mesozoic flora exhibits marked changes 231 
Recapitulation 232 
Extension of the inquiry to other cycles of denudation 233 
Comparison of baseleveling with glaciation and submergence 234 
Introduction. 
The considerations here presented have grown out of the 
studies of river histor}' and denudation which form the newly 
developed branch of geology known as geomorphy, geomor- 
phology, or simply pli3 r sical geograph}'. It is one of the ten- 
ets of this school of geologists that certain plains of denuda- 
tion now traceable over wide areas have resulted from 
subaerial erosion. Not a few geologists, however, still main- 
tain the view of marine erosion which Kamsay was the first 
to advocate regarding these ancient, tilted and now generally 
*An address read before tin- Harvard Natural History Society at its 
April meeting, 1894. The paper in its present form lias been partly re- 
written, but it still retains a strain of the lecture style in which it was 
conceived. It is published with the view of promoting inquiry into thiB 
subject, with which it deals in a preliminary and necessarily superfi- 
cial manner. 
