DAVIS: MOUNTAIN RANGES OF THE GREAT BASIN. £37 
the formative period of each mountain range now seen, their records of un- 
observed fact might give a complete account of all the processes involved ; 
and it would then be perfectly clear whether the mountain ranges were 
carved fault blocks or not. In the necessary absence of such observers, 
we try to replace their records by our discoveries, and although our 
method of discovery necessarily has recourse to the imagination, the 
phenomena that we successfully discover are facts of only a slightly dif- 
ferent order from those of direct observation. We see certain forms im- 
printed in stratified rocks, and by reasonable mental process arrive at the 
conclusion that these are the remains of once living organisms. We see 
two groups of similar strata in similar sequence, and by reasonable men- 
tal process reach the belief that their present discontinuity is the result 
of what is called faulting. In both these cases, the inferred explanation 
is accepted by most geologists as of essentially the same order of verity 
as the observed fact, because it has now stood the test of repeated and 
minute scrutiny. In the case of the Basin ranges, interpreted as carved 
fault blocks, many geologists are at present by no means disposed to 
attach equal value to the existing facts of structure and form reached by 
direct observation and the supposed past facts of dislocation reached by 
mental inference. It is therefore appropriate that special attention 
should be here given to the method of inference by which the past facts 
are resurrected. 
It is the application of the combined inductive and deductive method 
here sketched, although always applied less consciously and completely 
in the field than could be wished, that has satisfied me of the essential 
correctness of the theory which eaplains the larger ranges of the Great 
Basin as well-dissected blocks of long-maintained faulting, continued 
into recent time. 
Evidence of Faulting along the Mountain Base. — The first elements for 
consideration in this problem are those which should, in a type example 
of a long-faulted, well-dissected mountain block, be expectably associated 
with the occurrence of a fault along the mountain base. 
The simplest and most manifest element of this kind is a nearly 
straight or but moderately curved base line, Figure 1, passing indifferently 
across or obliquely along the structure of the mountain mass which rises 
rather abruptly and continuously on one side, while a sloping plain of 
waste is spread out on the other. The simple continuity of the base line 
and the complete absence of rock outcrops on one side of it are essential 
consequences of long-continued block faulting, and are at the same time 
not characteristic of any other available geological process. As Emmons 
