• I SMITHSONIAN MISCEL1 \nioos COLLECTIONS VOL. 69 



places in iii'- canyon ni the Dry Cimarron, in northeastern New 

 \ 1 «\i. ... 1 1 rests with angulai unconformity on the older " Red Beds." 

 1 mi inn. 1 1 as recenl investigations tend to show that the Exeter maj 

 bi ' quivalent t<> the w ingate, il seems advisable to class it .is Jurassic, 

 1 athei iii. in 1 i 1. 11. 



1 n brief, i'k - w ingate oi Prisons and New Mexico seems to be the 

 southward extensipn ol iii> - lowei sandstone oi the I .1 Plata group, 

 and this sandstone is traceable eastward to the Rio ( rrande. East oi 

 thai rivet and on both sides oi the Rocky Mountain axis a sand 

 stone "i similai charactei and holding the same itratigraphic poai 

 tion seems to be equivalent to typical Wingate and lowei 1 .1 Plata. 

 ii o\ . in 1 in iii.nn places, but not in all, as fai east as Oklahoma. 



1 in- middle 1 .1 Plata <>i rodilto is traceable bj means of the lime 

 stone and gypsum eastward to the Rio * itande and is recognizable i>\ 

 peculiai lithologic characters in man) places farthei east. Ii seems 

 probable that the limestone and gypsum east oi t'i< - mountains above 

 the Exetei sandstone denotes the same horizon rhe gypsum is not 

 continuous foi great distances ii occurs in more 01 less restricted 

 lenses rhe thin limestone underlying 11 is more persistent and 

 o< . urs in pla< i"- where there is no gypsum, 



rhe uppei I .1 Plata ( Navajo) teems to be less persistent than the 



lowei formations ot the group it thins out in some places in the 



inn Mountain region ot western New Mexico and has not been 



found neai feme tt seems to have 1 representative in the Cerrillos 



section, but has not been reported from localities farther cist. 



PREP \k \ HON FOR JURASSIC SEDIMBN 1 \ HON 



rhe reduction oi the ancient Rock] Mountains, which had been 

 in progress during much oi Permian and all oi rriassic time, seems 

 to have reached -i stage oi advanced peneplaination b) the opening 

 oi the furassic period However, the region was still above sea level, 

 .nui erosion continued during .1 long interval which, with minoi 

 interruptions, lasted through Jurassic and I owei Cretaceous time 

 During .ill oi this nun- the greatei part of the North American von 

 tun-in w.i^ above sea level and exposed to erosion, 



it seems desirable in tins connection to attempt to picture the 

 physiographic conditions in the Southern Rock} Mountain Province 

 previous to furassic time, luim opnuon.it isfliecessarj occasionally, 

 in ordei to obtain tiu< best results, to stand off at .1 distance from a 

 problem and take -i comprehensive view of it in its relation to other 

 problems rhe constant tendency ot the investigatoi is to confine 



