Baselereling and Organic Evolution. — Woodworth. 233 
draw the conclusion that the peneplain gave the reptilian 
class an advantage over the marsupials and as yet lowly or- 
ganized mammalia of higher types. This may have retarded 
for a time the mammalia in their conquest of the lands. 
Without the occurrence of the conditions which produced the 
broad peneplain, the ongoing of the mammals might have 
been more quickly accomplished, but on what lines? 
Extension ok the Inquiry to othek Cycles of Denudation. 
If we admit the principle which I have endeavored to derive 
from the history of the reptilian group in Mesozoic times, we 
ought to be able to apply it to other fields in other times. 
The great unconformities which occur in the Paleozoic and in 
the earlier terranes of the Algonkian are, at least in part, ge- 
netically peneplains. Unfortunately our knowledge of land 
life prior to the Carboniferous is exceedingly meager. It is 
only when the processes that formed the peneplain have 
ceased to act upon it, through the incursion of the sea or the 
warping of its surface to form lakes, that the records of ter- 
restrial life are embossed upon these monuments of erosion. 
In the Carboniferous period there is reason to believe that 
land life was strongly influenced by geographic conditions 
peculiar to that remarkable epoch. There were lowlands with 
swamps and jungles ad libitum, and these were tenanted by 
the precursors of the reptiles of the Mesozoic, the early am- 
phibians; but the lowlands of this period which are preserved 
to us were submarine platforms built up to the baselevel of 
meteoric erosion, rather than old lands worn down to that level. 
Prior to the Carboniferous and probably also to the later 
Devonian epochs, a baselevel of erosion was worked out in the 
highlands of Scotland.* The Old Red sandstone lies almost 
horizontally on this ancient door. But though we know much 
concerning the flora and fishes of the Devonian, and a little 
regarding its insects, there is not enough well known to afford 
a satisfactory correlation of the kind we seek to make. It is 
interesting to note in the Old Red sandstone another ease of 
apparently freshwater or lake bedsf resting upon what ap- 
*Sir Arch. Geikie, Scenery of Scotland, second ed., London, 1887, p 
137, el seq. 
fConsull Sir A. C. Ramsay, "<>u the Red Rocks of England of older 
date than t he Trias." Quart. Jour. Geol.Soc, London, vol. xwn. pp. 
241-256; Sir Arch. Geikie, Text-book <>f Geology, second ed., 1885, |>. 
711; and I.e. Russell, Bulletin .v.'. U. S. Geol; Survey, p. 17 et seq. 
