406 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



they rest on the Lower Cretaceous. Also, the lavas do not dip away from 

 the dome as steeply as die underlying Cretaceous beds, but since the 

 lavas have been tilted, part of the doming followed their outpouring. 

 Furthermore, King (1937) points out, an anticline that has folded the 

 Permian and Cretaceous rocks in the Glass Mountains extends north- 



westward into the Davis Mountains, where it involves the Tertiary lavas. 

 The folds are definitely older than the normal faults that break the strata 

 in the Glass, Del Norte, and Santiago Mountains, and there offset the 

 lavas. The normal faulting appears to have taken place soon after the 

 lavas were poured out, possibly in Oligocene or Miocene time. 



