734 



VICTOR ZIEGLER 



has discussed the Boulder area in detail and has shown that in 

 this district also it fails to account for the local structural features 

 and is fundamentally as unsound here as it is at Golden. 



The accompanying sections show the writer's interpretation 

 of the structure at Boulder. Here, as at Golden, steeply dipping 

 strike faults have taken place parallel to the general trend of the 

 foothills monocline, which are responsible for the disappearance of 

 some formations and the notable decreases in thickness exhibited 

 by others. The writer will not attempt to discuss these faults in 



Fig. 9. — Sketch map of vicinity of Boulder (after Eldridge). Heavy lines indi- 

 cate faults. For symbols, see Fig. 2. 



detail. They resemble in every respect the faults at Golden and 

 affect the strata in a similar way, but to a lesser extent. They 

 are in absolute harmony with the manner of disappearance and 

 thinning of the various formations, with observed dip and strike 

 relationships, and do not postulate the extreme local subsidences 

 and elevations required of the older explanation (Fig. 10). 



Minor structural features. — Much minor faulting and folding, 

 some of it of eccentric type, characterizes the great monoclinal 

 uplift. Elsewhere 1 the writer has discussed this in some detail, 

 especially for the purpose of bringing out the relation existing 



1 Op. cit. 



