Baselcveling and Organic Evolution. — Woadworth. 227 
nance of the reptilian group, arises from the imperfection as 
yet of our knowledge concerning the extent and distribution 
of the plain of meteoric denudation of this date. It seems 
now clear that the baseleveling of the North American conti- 
nent was so widespread as to be admitted as capable of exert- 
ing the control which is here claimed for it.* In the case of 
western Europe the evidence is also good, if we interpret the 
records in the light of our present understanding of the part 
played in denudation by land waters. f These two fields are 
so far best known for their reptilian remains. The geology of 
South Africa is as yet too little known to attempt a correla- 
tion in that geological province. While the present evidence 
would seem to correlate the distribution of the dominant 
dinosaur group with the lowlands of the Mesozoic about the 
North Atlantic, future discoveries may not only modify but 
controvert this opinion. 
It was not until this paper was written that I became ac- 
quainted with the work of Neumayr on the geography and 
organic life of the European Jurassic andNeocomian periods. 
The fact pointed out by him that the upper Jurassic rocks 
extensively overlap those of the lower Jurassic, so that "the 
Lias was not deposited over an enormous part of the earth's 
surface," \ is paralleled by similar conditions on the North 
American continent in the middle Mesozoic :£ but in this 
western world the subsidence which followed these broad con- 
tinental conditions did not come until the upper Cretaceous. 
It is pretty clear that the period of development of the Jura- 
( retaceous peneplain was one also of broad continental condi- 
tions, a circumstance evidently favorable to baseleveling. It 
*See \V. M. Davis: The Osage RiverAnd i lie Ozark Uplift. Science, 
vol. xxii. 1893. pp. 276-279. 
Dr. ('. A. White: Correlation Papers Cretaceous, Bulletin 82, U. S. 
Geol. Survey, [time-hiatus before Lower Cretaceous] p. 136; also pi. 11, 
ibid., "A Summary of the published Cretaceous Sections For each re- 
gion" of the United States, showing time-breaks in Lower Cretaceous 
contrasted wit h deposil ion. 
s. F. Emmons: Orographic movements in the Rockj Mountains, Bull. 
Gepl. Soc. Am., vol. i. L890, pp. 269-279 (Jurassic land). 
+ 11. I». Woodward: Geology of England and Wales, flrsl ed., 1876, pp. 
399, 100. 
+Sir Arch. Geikie, Text-book of Geology, third ed.. 1893, pp. 895-897. 
5 Dr. ( '. A. White. Cm-relation Papers, Bull. 82, U. 8. Geol. Survey, p. 
199. , 
