CORRELATION. 65 
on the fact that, though differing lithologically from the Aubrey 
limestone (Carboniferous) of the High Plateaus, it is more like it 
lithologically than any other formation underlying the Cretaceous 
of this region. A possible hiatus between the Pinto formation (Cre- 
taceous) and the Homestake limestone (see p. 17) may account 
for the absence of Permian, Triassic, and perhaps Jurassic sediments — 
if the last named, indeed, be absent (see p. 16) — between the Cre- 
taceous and Carboniferous of this district. The weak features of the 
correlation are the absence of sufficient fossil evidence, the dissimi- 
larity of the Homestake and Aubrey formation, and the absence of 
Permian, Triassic, and Jurassic sediments with so slight a structural 
discordance. 
IGNEOUS ROCKS. 
Only the earlier trachyte and the tuffaceous rhyolite have been 
correlated with rocks previously studied outside of the district, 
namely, the "rhyolite" of Dutton's High Plateaus survey . a These 
rocks were examined on Brian Head, near the south end of the area 
mapped by Dutton as rhyolite, and were found to be composed of 
a considerable thickness of rhyolite underlain by a rather thin layer 
of dark scoriaceous material like some of the scoriaceous phases of 
the earlier trachyte of the Iron Springs district. Below this, as 
in the Iron Springs district, were found Tertiary limestones and 
conglomerates. Thus a general correlation with the lavas may be 
made on the basis of their superposition above the Tertiary lime- 
stones and conglomerates in the two districts. 
a Dutton, C. K., Report on the geology of the High Plateaus of Utah: U. S. Geog. and Geol. Surv. 
Rocky Mtn. Region, 1880, pp. 61 et seq. 
28463— Bull. 338—08 5 
