al 
432 J. Croll—Examination of Wallaces Modification of the 
the interior to the Atlantic ocean. It is crossed by a great 
number of small streams which have excavated shallow valleys 
in the homogeneous modified drift of the plain. Each of these 
little valleys is limited on the west or right side by a bluff from 
ten to twenty feet’ high, while its gentle slope on the left side 
merges imperceptibly with the general plain. The stream in 
each case follows closely the bluff at the right. There seems 
to be no room for reasonable doubt that these peculiar features 
are, as believed by Mr. Lewis, the result of terrestrial rotation. 
As the streams carve their valleys deeper, they are induced by 
rotation to excavate their right banks more than their left, 
gradually shifting their positions to the right and maintaining 
stream cliffs on that side only. 
Arr. L.—Examination of Mr. Alfred R. Wallace’s Modification 
of the Physical Theory of Secular Changes of Climate; by 
James Crouu, LL.D., F.R.S. 
[Continued from page 93.] 
Parr IL—Geological and Paleontological Facts in relation to 
: Mr. Wallace's Modification of the Theory 
Mr. Watiace’s chief, and indeed only real modification of my 
theory, is to the effect, as I have pointed out, that the alternate 
phases of precession causing the winter of each hemisphere to” 
be in aphelion and perihelion each 10,500 years would produce 
a complete change of climate only when a country was partially 
snow-clad. According to his view, when the greater part of 
Northwestern Europe was almost wholly buried under snow 
and ice, those glacial conditions must have continued, and per- 
haps have even become intensified, when the winter solstice’ 
moved round to perihelion, instead of being replaced, as I have 
- Maintained, by an almost perpetual spring. In_ short, Mr. 
allace’s conclusion is that, during the Glacial Epoch proper, 4 
warm and equable Interglacial Period could not have occurred. 
In the preceding part of this paper I have endeavored to 
show that physical principles do not warrant such a conclusion. — 
I shall now proceed to consider what the direct testimony 9 
Geology and Paleontology is on the subject; and I believe we 
shall find that the facts of Geology and Paleontology are as muc 
opposed to the conclusion as are the principles of Physics. 
On this point I may quote the evidence of a geologist who, 
more than any other, has devoted special attention to all point 
relating to Glacial and Interglacial periods. Prof. J. Geikie, 
after devoting upwards of 500 pages of his‘ Prehistoric Europe 
