174 GEOLOGICAL SUEVEY OF THE TEREITORIES. 



yerse may be observed, a northern dip of 25° being observed for a short 

 space, but soon flattening to 10° again. The whole slope north of Park 

 View seemed to indicate a continuation of this northern dip, carrying 

 the lignitic beds down into the low flat basin of the North Park. To 

 the west the abrupt palisade edges of the great lava-cap covering the 

 lignitic in that direction show, extending in a high promontory north- 

 ward into the North Park ; and here, also, a gentle northern dip seemed 

 to be apparent at a few points. 



Though a large dike and several smaller ones occur in Park View 

 Mountain, their connection with the topography is best shown in a hill 

 northeast of that mountain, and across the westernmost fork of the Wil- 

 low from it. These dikes vary from 5 to 30 feet in thickness, some being 

 apparently over five miles in length, and extending across the country 

 like huge broken walls. Where several intersect or occur near one 

 another, their combined resistance to erosion has formed a hill, every 

 spur of which contains a dike. Between the two mountains is the pass 

 for the Willow Greek trail over into the North Park. The accompany- 

 ing sketch-map. Fig. 17, shows the forms of these two points, and their 

 connection with the dikes. There are probably several large dikes 

 upon the northern spur of Park View, and on the hills to the northwest, 

 which are not indicated in the map, as they were not clearly seen. 



The dikes are of a very handsome porphyritic trachyte, a grayish 

 green micro-crystalline or granular paste containing, as the more 

 noticeable ingredients, numerous large, well-formed crystals of white 

 orthoclase, and short, well-formed, hexagonal crystals of a soft, dark- 

 green chlorite.* 



The lava capping Corral Peak has some peculiar features which 

 should be mentioned before leaving this lignitic area. The summit of 

 the mountain is a squarish, rugged mass, rising precipitously at the 

 south w^est end of a ridge that runs about three-quarters of a mile 

 northeastward from it, where it is crossed at right angles by an 

 equally long but excessively sharp ridge, trending nearly northwest 

 and southeast. This whole top descends steeply, especially on the 

 northwest and south sides, for several hundreds of feet to the lignitic 

 beds on which it rests. The northeast ridge, though not examined at 

 its base, appeared as if it were the dike through which the eruptive 

 matter found its outlet. This ridge rises a little higher than the 

 broader neck connecting it with the main point which rises some 500 

 feet above either. The sharp ridge and all the main top is composed 

 of a dark, nearly black or brownish-black, brittle basalt, which pos- 

 sesses a resinous luster on a fracture face because of the very large 

 proportion of olivine permeating the mass. This lava weathers very 

 peculiarly, breaking in thin flakes or slabs, sometimes shaly, usually 

 standing nearly vertical, with flat conchoidal faces, which meet along the 

 edges as do the facets of a cut-glass tumbler. These slabs are highly 

 phonolitic ; and in weathering, the surface sometimes looks like a red- 

 dish, even-grained sandstone. The columns which compose the western 

 precipice are remarkably well formed. Some of them are two or three 

 feet across, sharply cut generally into five sides, cross-jointed into 

 lengths of from a few feet to a few inches, with, on the upper surface 

 of each joint, an exceedingly well-formed convex spherical surface, 

 rising two or three inches above the surface of the joint, and with its 



circumference nearly tangent to the sides of the joint. A corre- 



, . *-^ 



* It is intended that a proper chemical examination of this lava, as ■well as of all 

 the volcanic aud other rocks that require it, shall be made to be used in the final report 

 of Colorado. 



