MAKVLNE.] GEOLOGY PAKE EANGE AND BLUE RIVER MOUNTAINS. 187 



lower ones, the average size of the very numerous feldspar crystals be- 

 ing, perhaps, from a quarter to one-half an inch. While much of the 

 matrix was greenish, some was olive-brown, and, though mostly fine- 

 grained, some was slightly vesicular, and a little was observed inclining 

 to scoriaceous. The following is a record of the section down the west 

 side of the hill, the thickness being obtained, as usual, by using an ane- 

 roid, ])acing, and estimation : 



Section of hill in Blue Elver Valley, eleven miles from Grand River. 



Nature of strata. 



Thick- 

 ness. 



Trachyte 



Slaty shales 



Coarse trachyte 



Shale 



Trachyte 



Slates, mostly shaly, very fine, blue-black, at center heavy bedded to 18 

 inches ; uneven and broken surface 



Trachyte ; somewhat porphyritic, but mostly fine, irregular, and some scoria- 

 ceous ; breaks of one and two feet across slates 



Fine shales 



Limestone, fine, compact, dark blue; beds eight inches thick, subjointed to 

 shaly ; brittle ; in part shales below 



Trachyte 



Shales ; dark, fine 



Trachyte 



Shale : 



Trachyte , 



Siliceous sandstone, white 



River. 



Feet. 

 1001 

 2001 

 100 1 

 25 

 110 



120 



10 



60 



10 



80 

 100 

 275 



20 

 150 



80 



Across the valley, eastward from the hill above described, on the west 

 face of the Williams Mountains, is a little projected ridge, apparently a 

 short dike, passing through the lower beds of the mountains. It is 

 indicated in section 5, and modifies the section of the range, here near 

 its highest point, by causing the lower bed to run farther out in a ter- 

 race form than in the usual mountain section, which shows the west face 

 as steeper, and more as in the dotted line. A few miles south, in a 

 steep east bank of the main river, a vertical trachyte dike was observed, 

 about a foot thick at the base, thinning to nothing about 80 feet u}^, and 

 so disappearing before reaching the surface, on which no indications of 

 it existed. 



THE PARK EANGE AND BLUE RIVER MOUNTAINS. 



Meanwhile, the Park range has undergone some change. The 

 rounded ridge has gradually risen until, near the base of the abrupt 

 slope up to its southern extension as a rugged range, it is at the timber- 

 line. The Cretaceous sandstones, resting on the ridge, are here cut up 

 more than nearer the Grand. A remnant caps the very summit of the 

 ridge, but greater erosion has cut much of the sandstones away, leaving 

 the valleys in the granites. Much of this erosion has been glacial. The 

 valley, which has the steep and rugged slope of the northern ridge of 

 the mountains rising from its southern side, and the more even-con- 

 toured massive ridge on its northern side, i. c, the first valley north of 



