GEOLOGICAL SUEVEY OF THE TEREITOEIES. 217 



direction by innumerable large and small veins, mostly of quartz, but a 

 few granitic. Xone of these are metalliferous, so far as I could ascer- 

 tain. At two or three points there are beds of trap-rock from 50 to 70 

 feet thick, which appeared at first sight to be dikes ; but, upon further 

 examination, it became evident that they lay conformably between 

 regularly-bedded members of the granitic series, and it seemed as if 

 they might have been deposited as broad sheets of lava, like those 

 which we have seen flooring the Snake Eiver plain, but deposited ages 

 ago in the bed of the ocean, where were then accumulating the sedi- 

 mentary sandstones which were metamorphosed into these granites 

 before the Silurian age began. But, again, the trap shows no columnar 

 structure, but is indistinctly laminated parallel to its walling x^lanes; 

 and this would seem to indicate that it might, when quite viscid, have 

 been forced with difficulty between the solid granites after their up- 

 heaval, and so have received its laminated structure, while between 

 walls of such slow-conducting power it did not take on the columnar 

 structure. Or it is possible that, having been deposited horizontally 

 among the sediments, as aforesaid, it may have lost a columnar structure, 

 originally possessed, during the metamorphism of the surrounding beds. 

 The trap weathers much more rapidly than the granite; so that its out- 

 crops are plainly marked and readily traced from a distance by a sharp 

 notch on the crests as well as by its debris on the slopes of the mount- 

 ain. One of these beds, which crosses the saddle just south of the 

 Grand Teton, was thus traced across the Great Canon, antl up the side 

 of its perpendicular western wall, where at least 2,000 feet high ; and its 

 termination was then capped by the Potsdam quartzite, showing that it 

 is at least older than that rock. Both this trap and its inclosing granites 

 contain much epidote, partly compact, partly crystalline, and. some 

 pyrite. Near to this bed of trap are two very noticeable beds of 

 granite, one being of the deepest flesh-red, the other almost pure white; 

 both contain very little mica. The white bed has its constituent minerals 

 much segregated; so that we find in some places large masses of i)ure 

 feldspar, (orthoclase,) cleaving with broad surfaces, and again fine speci- 

 mens of graphic granite, (pegmatite.) From a neighboring bed come 

 large masses of mica (muscovite) tolerably well crystallized. A few 

 small garnets were seen, but we found no large or particularly good 

 crystals either of this or of any other mineral. 



While the beds are generally so much disturbed as to prevent the ac- 

 curate determination of any regular or prevailing dip, yet the general 

 strike is approximately east and west ; and this has determined, to some 

 extent, the structure of the range. The spurs running east and west 

 from each crest-peak are each dotted with three or four subordinate 

 peaks, which would be thought large, if they were not belittled by their 

 larger neighbors. The sharp dips cause the north and south sides to be 

 extremely sharp — even sharper than the natural weathering of the 

 granites, if level, would have made them. The highest of them all are 

 visible from great distances in every direction, both on account of their 

 great elevation and by reason of the sharp depressions on either side of 

 them. From whatever point they may be seen, there is little danger of 

 mistaking their identity, their abrupt, pointed outlines being markedly 

 different from those of any other peaks of the region. From their prom- 

 inence, afibrding good landmarks for travelers, they have sometimes 

 been called the Pilot Knobs, (see Irving's Astoria, chap, xxix ;) but 

 the name commonly applied, from the earliest times, is that of Tetons, or 

 Paps. As only three of the peaks are usually seen at a distance, they 

 have been called the Three Tetons. There are really ten or more dis- 



