134 BULLETIN OF THE ESSEX INSTITUTE. 



and west across both branches of Cheyenne Creek, being 

 indicated in the topography and also in the contrast pre- 

 sented by the granite — dark red and brown to gray and 

 variable above, and a lighter, brighter red and coarser 

 texture below. The really striking exposure is on the 

 northwest side of South Cheyenne Canon, where it appears 

 as a perfectly straight, sloping and open crack or fissure, 

 with a southwest hade of 60° to 70° (from vertical). 

 The shear faces are plane, smooth or even polished, and 

 slickensided in the line of hade (southwest). The fissure 

 is six to fifteen inches wide and occupied by some broken 

 granite, but mainly by what appears to be the dike sand- 

 stone, though some of it might be comminuted granite. 

 Examination with a lens leaves no doubt that the filling 

 is chiefly the dike sandstone. This prominent shear plane 

 is clearly a feature or part of the Ute fault ; and was 

 probably once connected with the sandstone dike already 

 described which crosses the ridge between the two creeks 

 only a short distance below the fissure. 



On the northwest bank of North Cheyenne Creek the 

 sandstone dike crops with a breadth of certainly one 

 hundred feet. On the slope above is a very large and 

 prominent outcrop, showing a width of fully two hundred 

 and fifty feet (23). Neither wall is clearly exposed, but 

 the boundary on the southwest or granite side can be 

 readily traced by the float and also by the prospect holes. 

 The lower hole is in the sandstone only a foot or two 

 from the granite and shows an irregular streak of granite 

 six to twelve inches wide running vertically through the 

 sandstone and parallel with the wall. In the same hole 

 some of the sandstone appears to be glauconitic. Toward 

 the middle of the dike are some masses and layers of 

 conglomerate with water-worn quartz pebbles up to au 

 inch in diameter, exactly like what may be observed iu 



