WEST HUMBOLDT RANGE. 727 



summit of Santa Clara Peak just east of north of Star Peak. They have a 

 dip of about 30°, sometimes going down to 20°, and, in the case of the 

 actual summit, to 18°. 



On the w^st side of the range, there occurs well exposed in Humboldt 

 Canon a heavy body of distinctly bedded typical white quartzite, with 

 cross-jointings breaking into coarse angular blocks, which forms the summit 

 of the broad ridge northwest of Star Peak, and all the higher western slope. 

 Near the summit, it has a dip of 25° to 35° to the west. This is, in turn, 

 again overlaid by blue limestone, with dark bands near the top, so rich in 

 carbon as to make a fissile rock, and to soil the hand when touched. It 

 extends across the northwest corner of the range from Eldorado Canon to 

 Prince Royal, and is regarded as the lowest member of the Jurassic forma- 

 tion. The only fossils found came from the first small canon south of 

 Humboldt Canon, and belong to undetermined species of Montlivaltia and 

 Cardium, both genera generally recognized by palaeontologists as not occur- 

 ring earlier than the Jura&sic age. These limestones pass gradually into 

 thinly-bedded almost fissile slates of a dull earthy color, with narrow bands 

 of interstratified sandstone and bluish-gray limestone, the formation extend- 

 ing down to the plain. 



The thickness of the formation, from the top of the porphyroidal rocks 

 or Koipato series to the top of the overlying limestone on the west side of 

 the range, has been roughlj^ estimated at 10,000 feet; the section, as given 

 in detail, consisting of broad, alternating zones of quartzites and limestones 

 up to the base of the slates and shales of the Jurassic. It seems highly 

 probable that the upper belt of limestone may at some future time be shown 

 by palseontological evidence to consist entirely of Jurassic strata, the broad 

 normal quartzite belt below separating formations of distinct geological 

 age ; but inasmuch as forms so characteristic as Montlivaltia and Cardium 

 occur in the upper limestone, there need be no hesitation in placing the over- 

 lying shales in the Jurassic, although they have as yet proved barren of 

 organic remains. 



In the upper part of Humboldt Cafion occurs a diabase dike only a 

 few feet wide, penetrating the white quartzite at a high angle, in a line 

 nearly parallel to the strike of the beds. It stands out prominently above 



