162 The American Naturalist. [February, 
being composed of material of local origin, (2) a complete absence of 
that wear which results from maintained river, sea or ice action, (8) 
organic remains which are those of a land fauna alone, (4) by bone 
fragments free from all marks of gnawing. In order to account for 
these conditions as well as for the mode of distribution of the rubble, 
which appears to be from many independent centres, Mr. Prestwich 
offers the following theory. The Rubble drift is the result of the sub- 
mergence and re-elevation of a land surface from beneath deep waters 
after a temporary submergence. : 
According to the author, this submergence occurred at the close of 
the Glacial, or so-called Post-glacial period, and immediately preceding 
the Neolithic or recent period. The submergence affected western 
Europe and the Mediteranean coasts decreasing eastward. The Rub- 
ble-drift and osseous breccia are but slightly developed in Syria. In 
regard to the north coast of Africa, Mr. Prestwich doubts if the sub- 
- mergence extended beyond the Lybian desert, as there is no well de- 
fined proof of it in Egypt. 
The significance of the Rubble-drift has an important bearing upon 
an estimate of the lapse of time since the close of the Glacial period. 
Mr. Prestwich calls attention to this in his closing remarks, citing evr 
dence to show that Mr. Croll’s reckoning of 80,000 years is not sup- 
ported by the facts of geology. The position and character of the 
Rubble-drift shows that the transition from the so-called Post-glacial 
beds to the recent alluvial deposits is abrupt, and there is no absence 
of sedimentation or anything indicative of lapse of time between the 
two series. This conclusion is confirmed by sections of the Belgian 
caves. 
Neither is the Croll theory, in the opinion of the writer, warranted 
by archeological evidence, for “it is hardly probable,” to quote the 
author, “that Man, who showed himself progressive early in the Qualer 
nary period, could towards its close, have remained for, s&y 70, 
years, without further progress than that shown by Man of the = 
Stone period. There is nothing to represent, geologically, that ir 
period of time, nor have biologists been able to detect any n 
structural differences between Paleolithic Man and Neolithic Man ™ 
support of such a conclusion. All the evidence tends to prove $ 
late Glacial (or post-glacial) Man, together with the great extinct Mam 
malia, came down approximately to within some 10,000 or 12,000 ee 
of our own times, and that the Rubble-drift marks the stroke of y 
pendulum when the Glacial period came to a close, and the Nec 
age commenced.” 
