TRIASSIC PORTION OF SHINARUMP GROUP loi 



marine-fossil horizon of the Jurassic and that of the " Permo- Carbon- 

 iferous " (I I ) . The upper, sandy portion of his Triassic section clearly 

 includes the White and Vermilion Cliff sandstones, although they 

 are not so named. The lower portion is described in general terms as 

 "variegated, saliferous, and gypsiferous clays." 



In the midst of the clays is a bed of conglomerate. The lower shales were 

 somewhat eroded by the current which spread it, as is shown by the inequality 

 of the surface on which it rests. Its thickness is variable, and it is not universally 

 present; but its persistence over large areas is nevertheless such as to excite won- 

 der. In the conglomerate and in the superjacent clays are sihcified tree trunks 

 in great numbers. The fossil horizon discovered by Mr. Howell near Toquer- 

 ville, and another that was noted south of Kanab, are lower than the Shinanmip 

 conglomerate (ii, pp. 175, 176). 



The Shinarump conglomerate appears to be definitely placed in 

 several detailed sections published by Gilbert, between "variegated 

 gypsiferous clays with silicified wood," above it, and "chocolate 

 gypsiferous clays," below (11, pp. 158-60). On Paria Creek and at 

 Jacob's Pool, Arizona, unconformities by erosion were noted below 

 the conglomerate, but of no great extent, and Gilbert laid no special 

 stress on the importance of the break indicated. Jacob's Pool is 

 between Kanab Greek and the Paria, at the south base of the Paria 

 Plateau. 



Marvine speaks incidentally of "a conglomerate of siliceous 

 pebbles, the Shin-ar-ump Triassic conglomerate of Powell" (19, p. 

 215). He apparently saw this bed only near St. George in Utah, 

 near its western limit of outcrop, and on the Little Colorado, in 

 Arizona. 



Howell seems to have practically followed the Shinarump con- 

 glomerate for several hundred miles. He says: 



The conglomerate bed to which Mr. Powell has given the name Shinarump 



is a very singular formation Having a maximum thickness at St. George of 



one hundred feet, it seldom exceeds forty or fifty to the east, but is coextensive, 

 so far as I know, with the Trias of the Colorado Plateau. Occasionally it is little 

 more than a coarse sandstone, and sometimes thins out to eight or ten feet, but 

 never have I passed that horizon without seeing it. One of its constant features, 

 almost as constant as its existence, is the great amount of silicified wood which it 

 contains (13, p. 283). 



Just below the ledge of the conglomerate, near Toquerville, in 



