512 INDEX TO THE STEATIGRAPHY OF NORTH AMERICA. 



The limestone conglomerates x)f the lower Dolores contain scanty but very widely dis- 

 tributed fragments of bones and teeth belonging to vertebrate animals. Much less frequently 

 invertebrate and plant remains of identifiable character occur in the same strata. The verte- 

 brate 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 

 Palaeoctonus of Cope. It is probable that the belodont, remains belong to the genus described 

 by Lucas under the name Heterodontosuchus ganei, or to allied forms. Poorly preserved out- 

 lines of Unio have been seen in several places and a small gastropod 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. 



Tracing the various strata from the San Juan district west and north in the 

 plateau country, through the work of Peale and Spencer, Cross"'" identifies the 

 Dolores formation in the Dolores, San Miguel, and Sinbad valleys. 



Below the La Plata, distinguished by Spencer, there occurs a much deeper red sandstone 

 formation, vermilion or brick-red in hue and corresponding to the upper division of the Dolores 

 as it has been described in this paper. Apparently the lower part, characterized near the San 

 Juan Mountains by the variable strata carrying fossiliferous limestone conglomerate, is not, 

 on the Dolores, markedly different from the upper in texture or color. Spencer has found 

 limestone conglomerate rich in bone fragments in several places, and on La Sal Creek this 

 horizon was but about 100 feet below the La Plata sandstone. The total thickness of the 

 nearly uniform Dolores formation is about 1,000 feet in the neighborhood of Sinbad Valley, 

 while much less in other localities. 



Over certain areas of the Uncompahgre Plateau in western Colorado the 

 Triassic is lacking, probably in consequence of pre-Jurassic erosion. ^'^"^ Northwest 

 of Grand River in Utah, however, the strata appear with the characteristics (5f the 

 Dolores formation. Cross ^*'"' gives the following section measured by W. H. 

 Emmons and L. H. Woolsey: 



Section near Grand Biver, opposite Moab, Utah. 



Top Feet. 



32. Sandstone, massive or shaly, dark red at base and bright red at top 20 



31. Shaly, conglomeratic sandstone, reddish limestone pebbles, the size of a pea or smaller, with 



few bone fragments 6 



Dolores Triassic. 



30. Sandy shale, red and green 5 



29. D6bris slope, of red shale fragments. 20 



28. Limestone conglomerate, with a few inches of limestone at top, fossil wood, and bone frag- 

 ments; pebbles less than 2 inches diameter 10 



27. Sandstone, gray, massive 20 



26. Limestone conglomerate grading into sandstone 1^ 



25. Sandstone, gray, massive becoming shaly near top 23 



24. Calcareous sandstone and fine-grained conglomerate mainly sandy, with conglomerate near 

 base and top. Pebbles of limestone and sandstone with occasional bone fragments; pebbles 

 vary from size of peas to several inches 9 



Permian (?). 



23. Red sandy shales, alternating with sandstone 8 



22. Conglomerate, containing pebbles of limestone and sandston* 1 



21. Sandstone and shale alternating, red and green, the shales sandy and friable 35 



Hermosa Pennsylvanian. 

 20. Blue limestone, weathering dirty buff, near top a layer contains pipe coral 10 



