G. K. Gilbert—Earthquakes of the Great Basin. 49 
in diminishing one difficulty it increases another, as will pres- 
ently appear. 
The second feature of joint structure which occasions dif_i- 
culty with the earthquake theory is that the angle of intersec- 
tion of coexistent systems is sometimes very small. Mr. Jukes, 
in his Manual, mentions 5° as a measured angle; and,.without 
being able to cite measurements, the writer believes he has 
observed angles as small as that. The considerations set forth 
in the preceding paragraph sufticiently explain how this phe- 
nomenon constitutes a difficulty. 
If these two features can be satisfactorily explained, there. 
seems no bar to the substitution of the earthquake theory for 
those previously entertained. : 
Art. XI.—A Theory of the Earthquakes of the Great Basin, 
: with a practical application; by G. K. GILBERT. 
[From the Salt Lake Tribune of Sept. 20, 1883.] 
| 
turbed. The uplifted part of the crust is the mountain, and 
the storms carve out its cafions; the unlifted part remains a 
lowland or valley, and receives the debris washed out from the 
‘Cafions. 
A mountain is not thrown up all at once by a great con- 
vulsive effort, but rises little by little. The subterranean 
upthrust is continuous and slow, and would produce a continu- 
ous upward movement of the mountain if the mountain’s 
