102 The America?i Geologist. August, i899 
those they see at \vork in the world around them. And per- 
haps the frequent failure of physicists and astronomers to 
frame a satisfactor)- theory for grand changes of climate 
may sometimes have been viewed by geologists with a kind 
of secret satisfaction. 
"It seems likely, however, that in this matter they must, after 
all, be content to follow the guidance of the astronomer and 
physicist, seeing that their own science refuses, in this par- 
ticular at least, to yield as much assistance as would be desira- 
ble. Nor, after he has sufficiently questioned all the natural 
causes with which his own peculiar studies have made him 
familiar, ought the geologist to feel surprised that these some- 
times fail to explain the phenomena that come under his cog- 
nizance. There is no hard and fast line separating the domain 
of one science from that of another, and as the circle of knowl- 
edge enlarges boundary divisions become more and more diffi- 
cult to determine. Perhaps of no science is this more true 
than that of geology. At one time the investigator into the 
past history of our globe had the field almost entirely to him- 
self, and the limits of his study were as sharply defined as if 
they had been staked ofif and measured. Now, however, it 
would be hard to say on which of the territories of his scientific 
neighbors he must trespass most. He cannot proceed far in 
any direction without coming in contact with some worker 
from adjacent fields. His studies are constantly overlapping 
those of the sister sciences, just as these in turn overlap his. 
It will, therefore, only be a further proof of the unity of nature 
if those intricate problems which have hitherto baffled the ge- 
ologist should eventually be solved by the researches of astron- 
omers and the conclusions of physicists."* 
Chapter III. 
The Scope of the Problem. 
From the review made in the preceding chapter, and from 
the quotations given, we see that it cannot be said that there 
exist opposing schools of geologists advocating with any de- 
gree of unanimity any special interpretation of, or assigned 
cause for, past climatic variations. 
*The Great Ice Age, 3rd Edition, pp. 794-5- 
