140 W. O. nRORBY ARCHEAN-CAMBRIAN CONTACT IN COLORADO 



gulch the line of contact, exposed only at intervals and dipping 10 de- 

 grees to the east and southeast, curves to the north and west around a 

 high hill to the point where it is cut off" by the Ute fault. At two points 



N.W. 



S.E 



+J' + ++.+ 



1+ + + "*"++ + 



I inch = 2-^eeX. 

 Figure 3. — Contact broken by a Gravity Fault. 



N.W. 



S.E. 



+^ + 



[inch = 2.f eet. 

 Figure 4. — Contact broken by a Thrvst Fault. 



on the west side of the hill the contact is seen to be broken by minor but 

 very clear faults (figures 3 and 4). 



Returning to the east side of Fountain creek, the contact is found to be 

 well exposed on the south side of the small gulch between the quarr}" and 

 Rainbow fall, where it is involved in a sharp inverted flexure (figure 5) 



- -Red. 



. . White. 





+ 





+ + + . ++ + 



4- 



v-r^- 



:^-^:+-^^ 



Figure i>.— Ocerthrust Fle.riire of basal Cambrian Beds on East Side of Utc Pass. 



accompanied by obliteration of the bedding of the sandstone. Toward 

 the left (east) end of the upper limb of the fold the contact is broken in 

 a way (figure 6) to suggest both faulting and shearing, with injection of 

 the gray sandstone into the broken granite, and thus throwing light on 

 the formation of the sandstone dikes. The exposure here trends east- 



