TABLE MOUNTAIN 323 



Triassic occurs as slates, limestones, and quartzites of characteristic ap- 

 pearance. Igneous intrusives are more common than in the Humboldt 

 ranges, and include coarse diorites and granites. Folding, faulting, and 

 alteration of the bedrock complex are everywhere observable. 



The superjacent volcanics. — Neither flank of Table mountain carries 

 basalt, or any other member of the volcanic series inclined so as to form 

 the hill slope as on the east side of the Humboldt Lake range. In fact, 

 the flanks are of bedrock, while the top carries basalt, in a number of 

 layers, underlain in part, at least, by other members of the volcanic 

 series. The true state of affairs is misrepresented in the atlas of the 

 Fortieth Parallel Survey, where the basalt of Table mountain is made 

 to occupy the whole slope down into and along the floor of the valley 

 through a vertical range of 3,400 feet. From the mapping, one would 

 conceive of the basalt as flowing out of some elevated vent, after the 

 formation of the range, pouring down the sides 3,400 feet, and then flow- 

 ing out over the valley floor. 



Hypothesis of upheaval. — Reasoning by analogy for the purpose of get- 

 ting a working hypothesis, which may be tested later, we may consider 

 the volcanics of Table mountain the equivalents of the volcanics of the 



Figure 5. — Diagram illustrating the essential Character of Table Mountain Faulting. 



Humboldt mountains, laid down at the end of the great period of erosion 

 and before the uplift of the Humboldt range. If the Table Mountain 

 range suffered an upheaval analogous to that of the Humboldt range after 

 the outpouring of the basalt, this must have been brought about by lat- 

 eral faulting on both sides, with relative elevation of the range mass as 

 a whole, with slight and unessential tilting, as shown in the diagram. 



Test of volcanic distribution. — Character of the proof. If such upheaval, 

 with but slight tilting, is the true history of Table mountain, we may 

 hope to find basalt in the valley on the west side lying above the level 

 of the alluvial filling because of uneven settling of the valley floor. 

 That is, the valley block might be intersected by minor faults and thus 

 broken into secondary blocks, as we have seen is probably true of the 

 Humboldt Valley block, and as is distinctly the case in the Humboldt 

 Range block, and also, it may be added, in the Table Mountain block. 

 Fortunate^, we do find basalt in the valley, and its occurrence will be 

 presently described. 



