The Peneplain. — Davis. 233 
much as it preserves some excellent fossil peneplains; and that 
the stratigraphic as well as the physiographic method of inves- 
tigation yields abundant and accordant evidence of their occur- 
rence. 
B 5. Plains of /narine abrasion as well as of subaerial de- 
7iiidation are diseaj'ded. It is worth while to point out ex-^ 
plicitly that all these districts which have been for half a cen- 
tury past explained as uplifted and dissected plains of marine 
denudation (or of marine abrasion) by geologists and geog- 
raphers in many parts of the world are to be otherwise inter- 
preted by those who adopt P rofessor Tarr's argument. The 
even skyline, discordant with structure, has been the leading- 
evidence for plains of marine denudation ever since it was in- 
troduced by Ramsay in his description of the hills and moun- 
tains of South Wales. For this reason it has seemed to me 
that others than those who accept the peneplain or subserial 
theory should have had more consideration in Professor Tarr's 
article; and for the same reason I have felt free to mention 
here certain denuded regions which have been interpreted as 
plains of marine denudation by the authors I have quoted. 
The marinists and the subserialists differ as to the agef\Cy^ 
by which an elevated region may be worn down to a nearly 
featureless plain, a little below or a little above sea level ; but 
they are unanimous in recognizing the necessity of such 
plains when uplands of even skyline exist in regions of disor- 
dered structure. All such plains are swept away as fictions by 
Professor Tarr's argument; for although he says little about 
plains of marine denudation and confines his attention almost 
wholly to peneplains, it must be rem.embered that these terms 
(plain of marine denudation and peneplain) are in nearly all 
cases hardly more than different names for the same thing. 
If the whole truth were known, it is probable that one or 
the other name might be appropriately applied in this or that 
case, but it is seldom that anyone has succeeded in convincing- 
all his contemporaries that he could distinguish a Jjlain of 
marine denudation from a peneplain, or vice versa. On the 
other hand, all regions, heretofore explained as having passed 
through the condition of abraded or denuded plains, would be 
explained as never having reached a form of faint relief, if 
Professor Tarr's alternative theory be accepted. It therefore 
demands careful consideration, to which we may now turn. 
