11)0 



STKATKIUArilY. 



At tlu^ rlosf ul" ('jiriionirt'i-ijus tiiiii's or ('.-irlicr. the .IciiU'Z .Moniilaiiis 

 woro uplif It'll, and associated with their d{M-elopiiieiit are to he found lar,i;o 

 intrusions of jiranites and porphyries ocenpyin.i;- an axial positicni. During 

 the period of ni(mntain linildin.u- The western tlank of the JeuieK Avas 

 faulted olf. Thi se mountains were suiise(inently siu-rounded liy a shallcjw 

 .'ui-assic sea, i]i which were deposited red sandstones and shales to a 

 thickness of Li.dii'i feet. Then came the Jurassic revolution. The moun- 

 tains were r( -elevated and tlie Jurassic strata to the west of the moun- 

 tains wei'e faulted and tilted to a nearly vertical position. At this time 

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

 olitic sheet which now on the plateau covers the .i;ranite porphyritie core 

 of the Jemez range, over which these sann- volcanoes, at a later time. 



