256 The American Geologist. April, i893 
evidence of a former base-level plain which is naturally less dis- 
tinct toward the north where subse(£uent elevation and denuda- 
tion have been greater." * 
6. Co7)ipletlon of the Cretaceous Cycle. The elevation which 
closed the Cretaceous cycle of development was of late Cretaceous 
or early Tertiary date. The occurrence of Cretaceous rocks un- 
conformably lying upon the elevated base-level at many points 
proves that the elevation could not have taken place until the end 
of Cretaceous time. 
The date of the completion of the process of base-leveling was 
not the same in all places, but varied according to the hardness of 
the rocks. In New Jersey! the base-leveling of the Triassic area 
was completed before the deposition of the Cretaceous beds, i. e. 
by the end of Jurassic time. The Cretaceous beds here over-lie 
unconformably a plain formed of the ])eveled edges of inclined 
Triassic sandstones. The base-leveling of the harder cr^'stalline 
rocks of the Highlands was not completed until the end of Cre- 
taceous time, for the material composing the Cretaceous beds was 
largely derived from the highland crystallines. Over the interior 
basin the rocks are relatively soft and the Cretaceous base-level 
appears to have been essentially completed before the deposition 
of the Cretaceous beds. The elevation of the base level, however, 
did not take place until the Cretaceous rocks had been deposited. 
The extension of the Cretaceous l)ase-level over the eastern 
Mississippi basin has now been considered and remnants of it have 
been found in widel}' separated parts of the basin. Probably be- 
fore the close of the Cretaceous period the whole of the eastern 
Mississippi was a lowland plain close to base-level, except in the 
southern Appalachian mountain region where the countr}" ma}' 
still have had considerable relief. The direction of the stream 
courses by which this erosion was accomplished has alreadv been 
Considei;ed in discussing the post-Carboniferous drainage. 
111. The Tertiary Cycle. 
1. The elevation of the Cretaceous hase-level. At the close of 
the Cretaceous or commencement of the Tertiary' there was a 
general elevation and warping of the Cretaceous base-level over 
' *1. c.,p. 221. 
f Bull. Geol. Soc. America, Vol. 2. The Geological Dates of Origin of 
Certain Topographic Forms on the Atlantic Slope of the United States 
— by W. M. Davis, pp. .554-5. 
