TUOUBITS MOUNTAINS. 523 



Magnesia 1.36 1,39 



Soda : 5.10 5.07 



Potassa 0.67 0.69 



Lithia : '. trace trace 



Carbonic acid 0.49 0.49 



Wetter 1.55 1.76 



99.88 99.96 

 Specific gravity 2.5-2.6. 



It will be seen that the rock stands rather high in silica for trachyte, 

 but this is doubtless owing to the presence of the chalcedony. A marked 

 feature is the large amount of soda and the correspondingly low percentage 

 of potassa. The analysis would indicate a hornblende-oligoclase trachyte. 



To the west of the Fountain Head Hills is a north and south valley- 

 like depression in the quartzite, in which the westward-flowing waters of 

 the Humboldt Eiver and the easterly-running streams at the head of Passage 

 Creek take their rise, suggesting the name for this group of hills. It con- 

 sists of a series of low rounded hills, whose underlying rocks are masked by 

 surface-accumulations of gravel and ddbris. The few outcrops shown indi- 

 cate that it is probably occupied by the beds of the Weber formation. 



TucuBiTS Mountains.— The Tucubits or Wild Cat Mountains form 

 a northern continuation of the East Humboldt line of elevation. They 

 consist of a mass of easterly-dipping quartzites and limestones, which, toward 

 the southern end, have been much faulted and dislocated, so that it has not 

 always been possible to trace the direct continuance of the beds. In its 

 northern portion, as represented on the map, where some of the peaks attain 

 a considerable elevation, it is formed mainly of bodies of quartzite, contain- 

 ing thin beds of curiously-banded cherty material, black and green in color, 

 representing the horizon of the Weber Quartzite Along the western base 

 are exposed heavy bodies of blue limestone, whose strike is somewhat 

 to the west of the trend of the range ; greater thicknesses are observed as 

 one goes south, and they were principally studied in the section exposed 

 by the canon of the Humboldt River called Emigrant Canon. 



In the exposures along the western face of the range, particularly at 



