72 ANNALti NEW YORK ACADEMY OF SOIENCEi,' 



of the Uiicompahgre Plateau, and partly in a lower southward facing 

 cliff a short distance farther north. 



A short distance west of Mack the river turns sharply to the south, and 

 cuts across the formations, giving complete sections of several of the 

 formations. 



Eiggs (1901, 4) describes the Morrison (McElmo) beds near Fruita 

 as a series of four principal members, aggregating 600 to 700 feet in 

 thickness. The lowest of the four he assigns to a marine origin. It is 

 100 to 120 feet in thickness, consisting of bluish-gray, gypsum-bearing 

 clays, with thin layers of fine-grained sandstone, and very thin layers of 

 nodular limestone. This division grades into the second, which he 

 assigns to a fresh-water origin. The second division contains no lime- 

 stone, and consists largely of homogeneous and massive clays. A ledge 

 of fine-grained sandstone occurs near the base. The second division is 

 about 100 feet thick, and consists of greenish clay shale, containing occa- 

 sional ledges of green sandstone and a iew layers of clay nodules. Con- 

 spicuous banding is not present. The third division consists of a' darker 

 zone containing frequent ledges of cross-bedded sandstone. This series 

 is 40 to 50 feet thick. The sandstones vary from fine-grained to coarse- 

 grained, and from thin layers to massive layers. They are often rich in 

 iron and brown in color. In places this division is entirely absent. The 

 fourth division consists of variegated clays 300 feet or more in thickness, 

 characterized by brilliant coloring and conspicuous banding. "The alter- 

 nation between green and purplish bands does not mark any variation in 

 the nature of hardness of these massive joint clays." Thin layers of cal- 

 careous nodules and sandstones occur. Nodular gray sandstone and thick 

 ledges of cross-bedded sandstone, and lenticular masses of sandstone occur 

 locally. 



Lee (1912, 6) has described the Morrison (McElmo) 1ieds in the Grand 

 River region as a variegated sandstone and shale formation lying between 

 the red beds and the Cretaceous beds. The formation here has a thick- 

 ness of 682 feet. The upper limit is marked by an erosional uncon- 

 formity. The formation is divisible into two general divisions which 

 are distinct litliologically, but still represent continuous deposition. The 

 lower member [Nos. 9-17 in section] consists principally of even-bedded 

 flaggy sandstone. This is the series Eiggs referred to as the marine 

 Jurassic. It contains some limestone. The upper member [Nos. 5-8 in 

 section] consists principally of variegated shale with a coarse conglomerate 

 near the top. 



The following section of the Morrison (McElmo or Gunnison) forma- 

 tion is given by Lee : 



