TJic Peneplain . — Tarr. 353 
feet."* This levelness is in spite of irregularity of rock \ 
"structure. "f No extensive peneplains are known to exist 
at the present time in any part of the earth, but many are 
inferred from the crest lines of old mountains, which are be- 
lieved to represent the remnants of dissected ancient pene- 
plains, produced during some previous geographic cycle. It 
is this conception of a peneplain which is discussed here, and 
for typical illustrations the peneplains of New England and 
New Jersey are selected, because they have been most fully 
studied and discussed, and rest upon the firmest basis. 
General Acceptance of the Peneplain Idea. — Few new 
theories have been so rapidly and uniformly accepted in this 
country as that of the peneplain suggested by Prof. W. M. 
Davis about nine years ago. \ Indeed its acceptance has be- 
come so universal and indiscriminate that the author of the 
explanation has found it necessary to caution his followers 
against rashness of conclusion, and to call for a more careful 
study of specific cases. § As in the case of most new ideas 
the follow'ers have gone beyond the originator, and it is per- 
fectly apparent that a great many of the so-called peneplains 
which have been described rest upon very much less secure 
basis than the types to which Prof. Davis has called especial 
attention. In this country many have evidently accepted 
Prof. Davis' explanation without question, and applied it to 
very doubtful cases, j 
Improbability of tlie Peneplain Explanation . — So far there . 
has been no extensive peneplain of recent date, nor even an ' 
approximation to one, found on the earth's surface in regions 
of folded rocks. Yet if we may judge from the evidence ad- 
duced by the modern workers in physiographic geology, pene- 
plains have been produced again and again at various times 
in the past. That is to say, during some past times there 
*Davis: Bull. Geo). Soc. Amer., 1896, vol. VII., p. 393. 
" fDavis: Am. Journ. Sci., 1889, ser. III., vol. XXXVII., p. 430; 
Proc: Boston Soc. Nat. Hist.. 1889, vol. XXIV., p. 2>7Z\ Nat. Geog. 
Monog., 1896, vol. I., p. 271. 
jAm. Journ. Sci., 1889, ser. IV., vol. XXXVII., p. 430. 
§Bull. Geol. Soc. Amer., 1896, vol. VII., pp. yj-j-y^. 
ll I feel free to speak upon this point, since I have been guilty 
of the same error, having described as a peneplain in Texas some- 
thing which may perhaps be a plain of marine denudation. See 
Proc. Phila. Acad. Nat. Sci., 1893, p. 317. 
