86 E. ORTON—GEOLOGICAL PROBABILITIES AS TO PETROLEUM. 
contributions of inestimable value to the well being and particularly to 
the comfort of the human race. 
In this modern development the new world has taken the leading part. 
What may be called a distinct branch of mining engineering, namely, 
the art of drilling deep wells, has grown out of it here. This art comes 
into close relations with the science of geology. It is hard to say at the 
present time which is the more indebted to the other, the art or the 
science. Each gives and each receives. 
The crust of the earth contains but few mineral productions that 
awaken such widespread interest as the bituminous series. The search 
for oil and gas is attended with much of the excitement that goes with 
the search for the precious metals, and success is in many cases as amply 
rewarded in the one as in the other. 
Geologists, especially if they concern themselves with the practical 
applications of their science, are constantly called on to answer ques- 
tions with regard to petroleum, its probable presence in any given local- 
ity, its modes of origin and accumulation, the duration of its supplies. 
They have recognized these new demands, and discussions bearing on 
such questions have made large additions to the literature of the science 
during the last forty years. These discussions are still in progress, and 
important contributions to our knowledge of petroleum and its deriva- 
tives are being recorded in our own day. 
In view of these facts, and despite the well worn and hackneyed nature 
of the theme, I feel warranted in asking you to follow me in a brief re- 
view of the geological probabilities as to petroleum. I use the modest word, 
probabilities, in this connection because it seems in all respects the 
proper word. Geology is a historical science, and but few demonstra- 
tions of the sort that carry mathematical certainty find place init. We 
have only probabilities as to all the dates of the science; for example, 
as to the date of the end of the Glacial period, let alone its beginning ; 
as to the date of the advent of man. Nay, more, we have only proba- 
bilities as to the weightier themes of geology; as, for example, the cause 
of glacial periods, the eruption of voleanoes, the formation of mountains, 
the condition of the interior of the earth. By what right, then, should 
we expect certainties on a subject that is one of the last to be considered 
in geology, and that is, by its very nature, complicated because of the 
fact that the geologist must depend upon the chemist for the ultimate 
decision of many vital points in the investigation? But I must remind 
you that there are probabilities and probabilities in geology. In other 
words, geological probabilities are of different orders. Some of them are 
so strongly supported that they count for certainties with many minds. 
In what respect they could be strengthened by subsequent discoveries 
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