318 G. D. LOUDERBACK — STRUCTURE OF THE HUMBOLDT REGION 



on the west slope near the southern end of the Star Peak range. This 

 locality was visited to determine, if possible, the relation of the granite 

 to the Mesozoic sediments. Rocky canyon is the easiest place to reach 

 the granite. After climbing a long alluvial cone, the granite is met 

 about half a mile within the true canyon, the western flank of the range 

 being made up of bedrock sediments, chiefly limestones. 



The rock that lies next to the granite, where the contact was studied, 

 is a kalksilicate-hornfels, which is banded and carries some carbonate. 

 It is only about 50 feet thick, and may be traced into a perfectly con- 

 formable series of well stratified drab to pale gray limestone, partially 

 recrystallized. These dip some 66 to 70 degrees west for a hundred 

 yards or so, where after a slight contortion the dip flattens. 



The occurrence of the calcite-limesilicate hornfels on the contact, fol- 

 lowed by partially crystalline conformable argillaceous limestones, is in 

 itself, ordinarily, sufficient evidence of the intrusive character of the 

 granite. For completeness the following may be added : 



The contact is quite irregular. 



Separated chunks of hornfels were found imbedded in the granite in 

 two places. 



The hornfels carries thin granitic dikes up to several inches in width, 

 which are also found directed outward in the granite near the contact. 



The bordering limestones have steepest dip near the granite, and their 

 dip becomes less as they are farther and farther away. 



The Fortieth Parallel Survey geologists who considered the granite 

 Archean and thought that the Triassic lay unconformably over the 

 granite, explained the steepening of the dip by thrust of the limestone 

 against the unyielding granite mass. They also apparently observed 

 the granitic dikes without recognizing their significance : 



"In the limestones in the region of Wright's canyon* and the large canyon to 

 the north, are irregular veins of feldspar, with occasional but rare masses of milky 

 white quartz. "f 



The granitic dikes are made up of quartz and orthoclase, with no mus- 

 covite or ferromagnesian mineral visible to the naked eye. 



Time of granitic intrusion. — The granite is thus proved to be post- 

 Triassic, but it has not yet been found in contact with Jurassic sedi- 

 ments. The fact that the bedrock complex was greatly folded as a 

 whole at the end of the Jurassic period, the Triassic having been not 

 greatly disturbed before the deposition of the Jurassic, would make the 

 post-Jurassic period of folding the most natural time for the granite in- 



* Now called Rocky canyon in Lovelock. 

 -f-Hague: Fortieth Parallel Survey, vol. ii, p. 719. 



