448 J. M. BOUTWELL 
will be grouped with the overlying fossiliferous limestone as of Per- 
mian age. 
THAYNES FORMATION 
Name.—This formation is named Thaynes after a canyon whose 
deep and extended incision affords the best exposures of this forma- 
tion within the district. 
Character.—This is essentially a calcareous formation. It com- 
prises two parts separated by a red-shale member, each made up 
of limestone, calcareous sandstone, normal sandstone, and shale. 
Most of the true limestones are in the upper part, and the sandstones 
predominate in the lower part, though each type is found throughout. 
A very characteristic lithologic type occurring at many horizons in the 
formation is a dense, homogeneous, blue-gray, calcareous sandstone, 
which appears superficially to be a limestone, but on exposure to 
the weather loses its low calcareous content and becomes a medium 
fine-grained, brown sandstone. ‘These are among the richest fossil- 
iferous members of the formations, as is shown below. ‘These mem- 
bers, the abundant and characteristic faunas, and the red-shale mem- 
ber—the “‘ mid-red”’ shale—serve to mark this formation and to enable 
one readily to distinguished it from the Park City formation. Topo- 
graphically, the outcrop forms abrupt cliffs, and the dip slopes and 
basset edges, broad flat slopes. Its surface is brushy and ledgy. A 
number of partial sections were measured and studied with great care 
for purposes of correlation, identification, and structural proofs. 
No complete sections or exposures which were not complexly faulted, 
intruded, or metamorphosed, which would serve for a standard sec- 
tion, were found within the district. ‘The nearest point where suit- 
able exposures could be found was about 3 miles west, in the north 
side of Big Cottonwood Canyon, where in several parallel spurs this 
formation occurs in excellent unbroken exposures. The composi- 
tion of the formation in that section, including lithology, thickness, 
and fossil characteristics, is briefly stated below: 
SECTION OF THAYNES FORMATION (PERMIAN) IN BiG CoTTONWOOD CANYON 
Lithology 
Thickness 
in Feet 
I Sandstone, massive, even, fine-grained, basal member, Argenta formation. 
I Limestone, blue, locally sandy, fossiliferous . 
