Besides the overlying sandstone bed, the red marls are traversed 

 below it by a conglomerate, which is in some places of a bluish 

 tint. At some points it weathers to gravel, and near this horizon 

 the vertebrate remains occur. 



In review I give the following section of the Eocene rocks of 

 the region west of the Sierra Madre range: — 



Red and gray marls ( Wahsatch ) 1500 



Sandstone ( Group J 1000 



Green and black marls — Puerco group .... 500 



3000 



The following is an approximate estimate of the mesozoic beds 

 in the same region ; as they were not accurately measured, the 

 numbers will have to undergo revision ; their relative thickness is 

 nearly. as given : — 



Uncertain (concealed in the sage plain .... 500 



Cretaceous No. 4 1500 



Cretaceous No. 3 400 



Cretaceous No. 2 2000 



Cretaceous No. 1 . . . 500 



Jurassic .......... 600 



"Trias" (bottom not seen) . . . . . .1000 



Total 6500 



The mesozoic beds of this section (excepting some of the higher 

 members of the cretaceous) have been examined over extensive 

 areas to the west and south, by Messrs. Marcou and Newberry, 

 whose valuable reports accompany those of Lieutenants Whipple 

 and Ives, on the routes surveyed by them through Arizona and 

 New Mexico. The horizon here termed, after Hayden, "Triassic," 

 has been referred to this formation by Marcou also, who had the 

 opportunity of examining it in Texas and the Indian Territory. 

 So far as the latter region is concerned, I can confirm the identifica- 

 tion, having examined bones from the in beds of that country, 

 which appear to be those of Belodonts. Dr. Newberry terms it, 

 in Arizona, the u salt group," or " saliferous sandstones," referring 

 to it as probably including both Triassic and Permian strata. 



The formations here called Jurassic are partially included by 

 Marcou in his triassic series ; and are termed the " variegated 

 marls" by Dr. Newberry, who is inclined to refer them to the 

 Jurassic. 



June 28, 1875. 



