302 



University of California Publications. 



[Geology 



case of plutonic intrusives that the writer has had opportunity 

 of observing there is evidence of greater intensity of action. The 

 magma is usually more or less thoroughly injected into the en- 

 casing rocks along their structural planes or across the beds in 

 fracture fissures. The encasing rocks are usually shattered and 

 angular fragments are scattered out into the body of the irrup- 

 tive. There is usually abundant evidence of more or less dynamic 

 metamorphism independent of the contact metamorphism. These 

 phenomena are lacking in connection with the "Weary Plat bath- 

 olith. The rocks of the district are folded, to be sure, but they 

 appear to have been thus folded anterior to the batholithic inva- 

 sion, and the flexures are, besides, quite open. We must thus 

 conclude that the intrusive act was of a rather mild type and 

 that the pressures within the magma, which gave rise to the 

 invasion from below, were not far above the point of equilibrium 

 when it had reached this stage in its upward path through the 

 earth's crust. Perhaps this is only another way of saying that 

 we have here to deal with the summit of a batholith, the level in 

 the liquid column where its intrusive force was about spent ; 

 and that at deeper levels,, had they been exposed by erosion, we 

 should have had revealed to us the more commonly observed 

 phases of intrusive phenomena. 



If we adopt this suggestion we have in it an explanation of 

 the peculiar geomorphy of Weary Plat. This is a very even 

 slope everywhere underlain by the monzonite. It lies at the 

 headwaters of a very feeble desert stream, with no catchment 

 area behind it, so that we can not interpret the flat slope as due 

 to stream planation. It is more probable that the present sur- 

 face of the monzonite is nearly coincident with its original upper 

 limit where it was overlain by the soft White Pine shale. In 

 this view of the ease the geomorphic expression is strictly con- 

 trolled by structure and the structural feature involved is the 

 nearly flat contact plane between a batholith of hard rock and 

 the roof of an overlying soft rock.* If it were otherwise, then 

 the Weary Flat slope must be due to the planation of the mon- 

 zonite; but this is highly improbable, since there are no residual 



* Cf . The Geology of the Upper Kern -Basin, Bull. Dept. Geol. Univ. 

 Cal., Vol. 3, No. 15, pp. 312 et seq. 



