68 ANNALS NEW YORK ACADEMY OF SCIENCES 



In the present discussion the McEhno will be considered as related to 

 the eastern Morrison formation. The following descriptions are from 

 Cross (1899, 3) in the Tellnride folio of the United States Geological 

 Survey : 



The McElmo or Morrison formation in the Tellnride quadrangle is a 

 variable series of shales and sandstones, with the latter more prominent 

 than is usual in this formation. The thickness varies from 650 to 900 

 feet. The sandstones are generally fine-grained, quartzose, yellow or 

 gray, and usually friable. Some of the sandstone beds are massive and 

 reach a thickness of 50 feet. More often they are separated by shale 

 layers. Cross-bedding occurs in some of the sandstones. Many of the 

 sandstones contain small flat flakes of green shale. 



The shales or clays are reddish or greenish, or a mixture of both colors. 

 They are generally calcareous and sandy. Sandstone layers occur in the 

 shale. In following the formation along the walls of the San Miguel 

 Canyon a shale stratum may be found to change, within a short distance,, 

 to an alternation of sandstone and shale. The reverse change often occurs 

 in the case of sandstone beds. 



At the base of the McElmo in this area is a highly colored shale resting 

 on the La Plata sandstone. 



The following is a typical section of the McElmo formation in the 

 Tellnride area: 



Feet 



Shale 11 



Sandstone, rather fine grained 22 



Shale, sandy, with many thin layers of fine-grained sandstone 53 



Sandstone, coarse, grading into conglomerate of quartz and chert pebbles 



at base 24 



Shale, dull red or green, with subordinate thin bands of very fine-grained 



calcareous sandstone 155- 



Sandstone, coarse grained, cross-bedded 4S 



Shale 11 



Sandstone, massive 16 



Shale, red, with thin sandstone layers ; 55 



Sandstone, white 11 



Shale, red, with thin sandstone layers 29' 



Sandstone, white, cross-bedded 22 



Alternating red shale and gray sandstone 85 



Sandstone, massive in lower part, but with thin red shale partings above. 80 



Shale, sandy 32 



Sandstone 8 



Shale, sandy, chocolate colored in upper part, thin layers of sandstone in 



upper part 64 



l^otal 724 



