MAEvixE.] GEOLOGY VICINITY OF HOT SPRINGS. 163 



followed by the Graud Lake road, a better cross-section is exposed alouo' 

 the road as follows : 



Section of Cretaceous Xo. 1, near junction of Hot Springsand Grand Lalce roadie, entranc/' o1 



Middle Park. 



Nature of strata. 



Estimated 

 thickness. 



Strike cibout north 20° east, dip ahout 35° nortiiicest. 



Doleritic lava 



Covered 



Sandstone, white and yellow, fine, gritty, siliceous, iron-stained 



Covered, red soil, debris of soft brown sandstone, and near base of purple 



shale and some limestone 



Sandstone, massive, white, some cream-colored, red blotches, siliceoup, 



gritty ^ 



( red soil •. 



Covered < soil 



( debris of brown sandstone and fine cherty limestone 



Ridge ; white, fine, gritty, siliceous sandstone, some cream-colored and red. 



Covered, red soil, (red shaly sandstones ?) 



Coarse gray granite, considerable mica, obscure gneissic structure. Strike ^ 



north 35° east, dip 50°-80° southeast. 



Feet. 



15 

 150 

 125 



225 



SO 



50 



150 



100 



100 



60 



This section would indicate a thickness of about athousand feet for those 

 beds, and affords an example of the greater thickness which I suppose the 

 lower Cretaceous beds occasionally attain. But ten miles to the north- 

 west, at the Hot Springs, a thickness of only about 3G0 or 400 feet is in- 

 dicated, butthe same general characters are there found ashere. Thelava 

 forming the top is composed of a dull, dirty gray, fine granular matrix, 

 with numerous black, quite well-formed crystals of augite scattered 

 through the mass. It weathers a dirty brown, with narrow white seams 

 two or three inches apart, parallel with the bedding, and speckled with 

 black augite crystals, as well as by both rusty and white-colored spots. 

 It is i3rol3ably a dike occupying the line of junction between the hard 

 sandstones and the softer Cretaceous shales, which probably occur im- 

 mediately above, though they are not here exposed. At one or two 

 other points in the park the weak point between the sandstones of 

 !N"o. 1 and shales of No. 2 have afforded a very natural outlet for erup- 

 tive matter, and such is probably the case here. After passing across 

 this section the Grand Lake road leaves the stream, and, turning to the 

 right along the outcrop), passes ui> a small valley, having the little ridge 

 of dolerite lava on the right. From the lava ridge, and on either side 

 of the main stream, is a steep slope rising to the summit of a terrace. 

 The channel of the stream passes into this, cutting a sharp V-shaped 

 gorge, the east side of w^hich rises some 50 feet higher than the general 

 level of the west side. The material of this terrace thus cut through 

 by the stream is coarse angular debris, of highly micaceous schistose 

 gneiss, of the dirty-red and black-banded variety, and some granite. 

 On the summit some large masses indicate that these metamorphic 

 rocks are in place. These facts would indicate that a fault had been 

 passed ; one which had thrown the outcrop of sandstone just described 

 downward on the southeast side, bringing the granite upward on the 

 northwest side, as in the accompanying section, Fig. 11, the position of 

 which is shown by the line C D, Fig. 10. 



Passing on northwest, the coarse debris terrace is found to fall in 



