468 CROSS AND HOWE — RED BEDS OF SOUTHWESTERN COLORADO 



vary considerably, increasing from the mountains west and southwest 

 toward the Plateau country. 



Upper red sandstone member. — The upper member of the Dolores is 

 commonly a very even, tine grained, reddish sandstone, free from con- 

 glomerate, but variably shaly in different places. The shales are, how- 

 ever, always very sandy and there are seldom pronounced division planes 

 of great lateral extent. The bands of parallel, massive sandstone are 

 often 20 feet or more in thickness. The material is mainly quartz sand, 

 with a calcareous cement. In color this upper sandstone is usually 

 bright brick-red or vermilion, shading sometimes into purplish above and 

 a duller, darker red below. In texture this red sandstone is very much 

 like the overlying La Plata sandstone, and where the latter is highly . 

 colored the two formations seem sometimes inseparable, but the La Plata 

 is commonly orange or yellow in color when it departs from the normal 

 gray or white. 



The upper member of the Dolores is absent in the Ouray and parts of 

 the Telluride quadrangles, but presents an increasing thickness south- 

 ward through the Rico and La Plata quadrangles. Nearly 500 feet of 

 quite uniform sandstones were observed on the eastern flanks of the 

 La Platas. The variation in thickness and the disappearance of the red 

 sandstones to the north is due chiefly to the post-Dolores erosion. 



Fossils. — The limestone conglomerates of the lower Dolores contain 

 scanty but very widely distributed fragm en ts.of bones and teeth belonging 

 to vertebrate animals. Much less frequently invertebrate and plant re- 

 mains of identifiable character occur in the same strata. The vertebrate 

 remains have never been found as connected skeletons, or even closely 

 associated bones belonging to one individual. They are usually worn and 

 often broken. The most common fossils are the teeth of crocodiles and 

 dinosaurs. Material collected from many localities has been studied by 

 F. A. Lucas. The greater number of the remains belong to the belodont 

 crocodiles, while less numerous are those belonging to a megalosauroid 

 dinosaur, perhaps Palasoctonus of Cope. It is probable that the belodont 

 remains belong to the genus described by Lucas (28) under the name 

 Heterodontosuchus ganei, or to allied forms. Poorly preserved outlines of 

 Unio have been seen in several places and a small gasteropod shell has 

 been found in the Rico and La Plata quadrangles. According to Stanton, 

 the latter belongs to the genus Viviparus or to a closely allied form. 



The fossils first announced by Hills (20) from the Dolores beds were 

 found in the Telluride quadrangle, on the north side of the San Miguel 

 river, 1£ miles below the present site of the town of Telluride. Appar- 

 ently, the locality is unique in the number and comparatively excellent 



i tate opreservation of the remains found. These fossils were submitted 



