SOME UNSOLVED PROBLEMS IN GEOLOGY. 285 
the annual address before a large audience in the Westminster Church, one of 
the finest churches in the West, upon the subject : 
SOME UNSOLVED PROBLEMS IN GEOLOGY. 
It is not practicable to give the full address, as it would make at least thirty 
pages of the Review, but it is believed that the abstract given below covers its 
main points : 
Ladies and Gentlemen of the American Association for the Advancement of Science : 
There is no department of physical or biological science with which geology 
is not allied, or at least upon which the geologist may not presume to trespass. 
When, therefore, I announce as my subject on the present occasion some of the 
unsolved problems of this universal science, you need not be surprised if I should 
be somewhat discursive. 
Perhaps I shall begin at the utmost limiits of my subject by remarking that 
in matters of physical and natural science we are met at the outset with the 
scarcely solved question as to our own place in the nature which we study, and 
the bearing of this on the difficulties we encounter. The organism of man is 
decidedly a part of nature. We place ourself, in this aspect, in the sub-kingdom 
vertebrata and class mammalia, and recognize the fact that man is the terminal 
hnk in a chain of being, extending throughout geological time. But the organ- 
ism is not all of man, and when we regard man as a scientific animal we raise a 
new question. If the human mind is a part of nature, then it is subject to 
natural law, and nature includes mind as well as matter. On the other hand, 
without being absolute idealists, we may hold that mind is more important than 
matter, and nearer to the real essence of things. Our science is in any case 
necessarily dualistic, being the product of the reaction of mind on nature, and 
must be largely subjective and anthropomorphic. Hence, no doubt, arise much 
of the controversy of science and much of the unsolved difficulty. 
Fortunately, as a geologist, I do not need to invite your attention to those 
transcendental questions which relate to the ultimate constitution of matter. This 
record of geology covers but a small part of the history of the earth and the 
system to which it belongs, nor does it enter at all into the more recondite pro- 
blems involved ; still it forms, I believe, some necessary preparation at least to 
the comprehension of these. But if we are content to start with a number of 
organisms ready made — a somewhat humiliating start, however — we still have to 
ask. How do these vary so as to give new species ? It is a singular illusion in 
this matter, of men who profess to be behevers in natural law, that variation may 
be boundless, aimless and fortuitous, and that it is by spontaneous selection 
from varieties thus produced that development arises. But surely the supposi- 
tion of mere chance and magic is unworthy of science. Varieties must have 
causes, and their causes and their effects must be regulated by some law or laws. 
Now it is easy to see that they cannot be caused by a mere innate tendency in 
the organism itself. Every organism is so nicely equilibrated that it has no such 
