164 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



traced downwards. Their hade usually approaches the perpendicular, and, 

 as is common with the displacements in older rocks, slopes to the downthrow. 

 In the instance represented below, however, the hade is reversed ; this ex- 

 ample occurs in unconsolidated gravels and clays of the Lahontan series at 

 Mullen's Gap, on the western border of Pyramid Lake. 



r ■/ " ■■■ - ^ 



Scale of feet — vertical and horizontal the same. 



^ j> lb 



Fig. 25. — Keverse fault in Lahontan gravels. 



The upward bend of the strata on the heaved side of this fault may 

 perhaj^s be accounted for by assuming that the displacement has undergone 

 double movement. During the first, the block to the left of the plane of 

 fracture, as it appears in the figure, was the thrown block ; its downward 

 movement caused the ends of the strata of which it is composed to bend up- 

 wards, as is common in similar displacements in older rocks ; afterwards the 

 movement was reversed, and what was previously the thrown side was up- 

 raised beyond its former position. The faulting took place in tliis instance 

 previous to the deposition of the cross-stratified gravels represented in the; 

 diagram above the line of uiiconformability, as is proven b}' the fact that 

 the plane of fracture does not extend through them. The interval between 

 the disturbance causing the fault and the deposition of the superimjjosed 

 beds was short, as is evident from the absence of erosion along the surface 

 of uiiconformability. 



Another illustration of the minor displacements that occur in the 

 Lahontan sediments is given on Plate XXllI, Fig. A, which is remarkable 



