SANDSTONE DIKES OF UTE PASS. 117 



thick and hades southwest. An uncertain thickness of 

 granite separates this from a dike fifty and possibly one 

 hundred feet wide of undetermined hade. Both dikes 

 are entirely typical in lithological character, 1)ut in con- 

 sequence of the deep disintegration of the granite they 

 are not well exposed. The sandstone is the usual dull 

 red, blotched and spotted with white where the iron 

 oxide has been reduced and leached out ; and it seems 

 to be somewhat glauconitic. 



From this point a gulch extends northwesterly along 

 the line of the old South Park trail, l)etween the long 

 slope of disintegrated granite and the al^rupt, sharp- 

 crested hill of the Potsdam sandstone and Manitou 

 limestone, which still maintain a high northeast dip. 

 The indications are that the first dike mentioned follows 

 the bottom of the gulch and the fault-line closely. On 

 the col at the head of the gulch several irregular dikes of 

 sandstone, with a maximum width of at least forty feet, 

 outcrop obscurely in the granite ; and immediately above 

 on the northeast are the highly inclined Potsdam sand- 

 stone and red and gray cheily limestones, the lines of 

 snow-white chert in the lower limestone contrasting 

 strongly with the deep red matrix. 



The northwest-southeast ridge of sedimentary rocks, 

 which the fault-depression places vis a vis with the abrupt 

 border of the granite, is, within a distance of about one 

 and a half miles from Iron Spring Station, divided by 

 transverse gulches into four hills (1, 2, 3, 4). On pass- 

 ing down either of these gulches we see that the high 

 northeast dip due to the fault quickly gives way to the 

 normal dip of the region (S. E. 10°-15*^), and this rising 

 of the formations to the northwest brings the i)asal beds 

 above the present surface at the northwest end of the 

 fourth hill. 



ESSKX INST. BUI.LEriX, VOL. XXN'II 12 



