650 WHITMAN CROSS 
Colorado, is unquestioned, and all observers have referred it to the 
Trias. It is characteristically developed on Grand River. 
Below the Vermilion Cliff sandstone of the classic Plateau section 
comes a series of beds originally called by Powell (33) the ‘‘Shina- 
rump group,” and for it the early observers claimed the same wide- 
spread distribution as for the overlying formations. Referred as a 
whole to the Trias by Powell, it was long ago shown by Walcott (37) 
that the lower portion of the Shinarump group of the type locality was 
Permian (?). Our observations on Grand River show that the 
strata below the Vermilion Cliff sandstone, corresponding in position 
to the Shinarump, are of very different character from those of the 
typical section of that group. 
In the Red Beds paper (8), I suggested that the Dolores formation 
of Colorado includes diminished equivalents of the Shinarump 
group and Vermilion Cliff sandstone of the plateau province. With 
qualifications as to the Shinarump this view has been substantiated. 
The importance of the relations discovered on Grand River requires 
a preliminary review of the essential features of the Dolores formation 
as an aid to a comprehension of the new data. ; 
The Dolores formation of the San Juan region.—The name Dolores 
Formation has been proposed for the Triassic portion of the Red Beds 
of southwestern Colorado. It is now known to embrace but a few 
hundred feet of strata, with stratigraphic breaks, represented in some 
localities by definite unconformities, both above and below. In the 
San Juan country the Dolores consists of an upper, dark red, fine- 
grained sandstone, of variable thickness, in consequence of the 
pre-La Plata erosion just discussed, and of a lower sparingly 
fossiliferous succession of sandstones, shales, and peculiar con- 
glomerates. 
The thoroughly diagnostic element of the Dolores formation is a 
certain kind of fine-grained reddish or grayish conglomerate, occurring 
constantly at its base and repeated in variable development at several 
horizons in the lower 200 or 300 feet of sandstones and shales. The 
pebbles of these peculiar conglomerates are commonly very small 
in some places, resembling pisolitic grains, and appear to be derived 
from the breaking-up of limestone beds in process of formation; at 
least, they are not from the bluish fossiliferous limestones of the 
