150 W. O. CROSBY — ARCHEAN-CAMBRIAN CONTACT IN COLORADO 



developed in some cases as a tendency to concentric exfoliation, showing 

 that in Cambrian time this structure existed, as now, and influenced the 

 erosion of the granite. These rounded and in general more resistant 

 masses, as now exposed in the granite, vary from 1 to 6 feet in diameter. 



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- + + . 

 .+ + 



I inch = 3[ eet. 



Figure 17. — Residuari/ Hamviock of the Granite Surface. 

 Due to spheroidal structure. 



1 inch = 3f eet. 



Figure 18. — Residuary Hummocks of the Granite Surface. 

 Due to spheroidal structure. 



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1 inch = 3 feet. 



Figure 19. — Structure similar to Figure 18. 



They were usually left in relief on the eroded surface, but were some- 

 times worn out to form hollows. Fort}' feet farther west is a small 

 normal fault (figure 15), and 40 feet farther still an original irregularity 

 (figure 17). Then after 20 feet the contact is broken hy a small vertical 



