HOMES.] GEOLOGY OF MOUNT EVARTS. 11 



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 A sparse growth of stunted pines has taken root in the rocky slope and 

 on the crest of the ridge there are groves of full-grown trees. 



The examination of the basalts near the summit proved unexpectedly , 

 interesting. The masses of this rock are very irregular in thickness, 

 reaching in places 40 and 50 feet, their position in the strata, being very 

 irregular. They lie in rude sheets approximately with the strata, but 

 bearing the strongest evidence of their intrusive character. 



The irregular bed that outcrops along the crest of the ridge is in places 

 40 feet in thickness, but generally falls far short of this. Its position in 

 the strata points very clearly to its intrusive character. It does not lie 

 in any one horizon, but breaks across the strata at all angles^ crushing 

 the severed edges back upon themselves as shown in the drawing, Plate 

 V. It rests chiefly in a series of coal shales and sandstones in which 

 are very numerous leaf impressions. The shales are but little changed 

 by contact with the basalt, and where in actual contact are still brittle 

 and crumble under the hammer. The shales above the intruded mass 

 are also but little altered. 



In the heavier masses this basalt has a rudely columnar structure and 

 weathers down in very small angular blocks. In the thin tongues that 

 have been thrust out from the main mass into the surrounding strata 

 there is a tendency to form small prisms at right angles to the surface, 

 as shown in the figure; while the interior part of these tongues has 

 only a minute irregular jointage. 



The color of this basalt is, in the weathered surfaces a rusty brown, 

 but when freshly fractured a dark steel grjiy. It is fine grained and 

 compact and has no crystals distinguishable by the naked eye. The 

 strata which inclose this basalt dip to the northeast at angles of from 

 10° to ISC', tiie liue of the great fault, which defines their northern limit, 

 being about two miles distant. It seems probable that the intruded 

 basalts may have originated in or rather reached their present position 

 through this fault, the crushing of the strata indicating, generally, an 

 intrusion from that direction. Similar intrusions are very numerous in 

 all the strata bordering the fault line. (See Plate VI.) 



It may be well in this connection to give another illustration of the 

 intruded basalts which occurs also in the western face of Mount Evarts, 

 but farther south and within a mile of the mouth of the East Fork of 

 Gardiner Eiver, and within about 400 feet of the bed of the main 

 Gardiner. The rock is a pinkish-gray basalt (?) that weathers down in 

 crumbling heaps, but where freshly exposed is an exceedingly compact 

 and fine-grained rock. The mass is about 300 feet long by from 12 to 

 15 feet thick and appears in the face of a steep wall of dark shales and 

 laminated sandstones. It has been forced in between the yielding strata, 

 folding them up almost at right angles at the ends, as shown in the fig- 

 ure, Plate Yl. There is a decided alteration in the contiguous strata; 

 the shales and sandstones for a number of feet beyond the contact with 

 the intruded mass being changed to hard slates and quartzites which 

 break up in minute blocks. Other intrusions occur all along the face of 

 the wall that overlooks the caQons of the East Fork and are especially 

 numerous about the falls and on the south side of the valley. 



Having followed the crest of the mountain south from the previously 

 described outcrops of basalt, I soon reached the north edge of the great 

 sheet of rhyolite that rests upon the flat part of the summit. The north- 

 ern border of this sheet is pretty thoroughly obscured by soil and drift 

 deposits, and cannot be defined with accuracy, but the exposure on the 

 west front is simply perfect. The whole thickness of the sheet, some 

 80 or 90 feet, breaks oif in a vertical and overhanging clilf. The upper 



