1878. | Physiography. 681 
system greater and grander than ours will be formed, and that 
so the same thing will go on until all the matter of the universe 
is aggregated into one mass, and all the energy of the universe is 
converted into uniformly diffused heat. 
But here have transcended the powers of the human intellect. 
We have reached that thin atmosphere in which we can no longer 
build. We have traced the chain of causation as far as we are able. 
We have reached the Unknowable. When we seek to go further; 
when we inquire what is matter, what is force, what is the ether 
through which force acts on matter, what is the space in which co- 
existences are manifested, and the #me in which sequencesare mani- 
fested ; when we inquire what is consciousness, what is the shought 
by which we are able to trace to some extent the chain of causa- 
tion, we are met by alternative contradictories. We are in the — 
presence of the Mystery of Mysteries. Let us humbly, modestly, 
truthfully confess our ignorance. 
It may, perhaps, be said that there is much in the foregoing 
pages that is quite out of place in the Geological Magazine— 
much about wind and aqueous vapors, the Nebular Hypothesis 
and the Unknowable. But is it out of place? If there be any 
truth in my opening paragraph—that just as an artist has now 
and again to view his picture from a distance, so does the man of 
science have from time to time to take a comprehensive survey of 
his subject—No. In any consideration, however imperfect, of the 
work which Geology is doing for Modern Philosophy, we must 
weave that work into the general picture presented by the study 
of Nature. This I have attempted to do. In the place I have 
endeavored to point out the law of causation ; that all that we see 
about us has been caused in some way or other. In most cases, 
from the nature of the subject, this law of causation has been 
illustrated qualitatively ; but in the case of the formation of water- 
vapor the quantitative truth of the law has been indicated; and 
the law of the conservation of energy briefly alluded to. In the 
second place I have tried to show, as far as was possible in the 
space at my command, how the crust of the Earth has been built 
up by the mechanical agency of rivers, forming deltas, and the vital 
agency of simply-constituted creatures. By these two agencies 
nearly all the rocks have been formed, with the exception of salt, 
and, perhaps, magnesian limestone, which are due to chemical 
agency. By the action of earth-heat and other causes, however, 
