190 



STKATIGRArHY. 



At the close of (niijoiiiferons times or e.-irlier. tlie Jeiiiez Mountains 

 were uplifted, and associated with their develoimient are to l)e found large 

 intrusions of jiranites and porphyries occupying an axial position. During 

 the pei'iod of niminlain linilding ilie western tiank of the Jeniez was 

 faulted off. Tin se mountains were sui)se(iuently sm-rounded by a shalloAV 

 .lurassic sea. in which were depositwl red sandsttnies and shales to a 

 thiclaiess of 2.<KH) feet. Tlien came the Jurassic revolution. The moun- 

 tains were re-elevated and the Jurassic strata to the west of the moun- 

 tains were faulted and tilted to a nearly vertical position. At this time 

 the volcanoes near Pelado became active, and poured out the great rhy- 

 olitic sheet which now on the plateau covers the granite porphyritic core 

 of the Jemez range, over which the.se same volcanoes, at a later time, 



