276 CHARLES LAURENCE BAKER 
that all of the ranges of the Great Basin were of the block-faulted 
type, nor, as far as the writer knows, did he ever express the opinion 
in writing that the block-faults were all the results of tensional 
stresses. 
On the contrary, Gilbert expressly states, on pp. 61 and 62 of 
Vol. II, U.S. Geographical Surveys West of the tooth Meridian, 
the following: 
. . . . In the Appalachians corrugation has been produced commonly by 
folding, exceptionally by faulting; in the Basin Ranges, commonly by faulting, 
exceptionally by flexure. The regular alternation of curved synclinals and 
anticlinals is contrasted with rigid bodies of inclined strata, bounded by 
parallel faults. ‘The former demand the assumption of great horizontal diminu- 
tion of the space covered by the disturbed strata, and suggest lateral pressure 
as the immediate force concerned; the latter involve little horizontal diminu- 
tion, and suggest the application of vertical pressure from below. ... . It is, 
that in the case of the Appalachians the primary phenomena are superficial; 
and in that of the Basin Ranges they are deep-seated, the superficial being 
secondary; that such a force as has crowded together the strata of the Appa- 
lachians—whatever may have been its source—has acted in the Ranges on 
some portion of the earth’s crust beneath the immediate surface; and the 
upper strata, by continually adapting themselves, under gravity, to the inequali- 
ties of the lower, have assumed the forms we see. Such a hypothesis, assign- 
ing to subterranean determination the position and direction of lines of uplift 
in the Range System, and leaving the character of the superficial phenomena 
to depend on the character and condition of the superficial materials, accords 
well with many of the observed facts, and especially with the persistence of 
ridges where structures are changed. It supposes that a ridge, created below, 
and slowly upheaving the superposed strata, would find them at one point 
coherent and flexible, and there produce an anticlinal; at another hard and 
rigid, and there uplift a fractured monoclinal; at a third, seamed and inco- 
herent, and there produce a pseudo-anticlinal, like that of the Amargosa 
Range. 
Spurr’s general view that the present Basin Ranges owe their 
forms to folding modified by erosion, holds in part, but Spurr 
appears to have clearly recognized but one great deformation, 
the mid-Mesozoic, although he did mention the folding of Tertiary 
strata. He failed to recognize that the axes of later deformations 
often cut diagonally or at right angles across the axes of the mid- 
Mesozoic folding. The recognition of this fact was one of Louder- 
