PROGRESSIVE INCREASE OF VISCOSITY 543 
Whitewood limestone. Lowest Cambrian strata are reported by 
Jaggar, in a tunnel, on the north end of the mountain.t_ On most 
of the southern half of the porphyry, however, the intrusion reaches 
the Pahasapa limestone, while at the extreme southern end the 
Minnelusa sandstone is cut by the igneous rock. Near this latter 
locality a small mass of Cambrian sandstone was observed, so situ- 
Sn ey pee a4] SOND 
aI NIN AAS 
Sic F a s vn A. 
as 
= wD 
: : x on 
. : f = Skee 
ES <5 V=75\ es SAS 7 ' a 7 
Sof) Ni en t o ~ ~S FES eA ee , EN: Sul ! = ~ 
PB aed MeN, EN CATING NS NONE GN eI NI SvSees 
Fic. 1.—Geologic map and cross-section of Crow Peak (Paige): DS, sandstone 
of Deadwood formation; WL, Whitewood limestone; EL, Englewood limestone; 
PLS, Pahasapa limestone; MS, Minnelusa sandstone. ; 
ated that only faulting could explain its presence. As figured 
by Jaggar, both in plan and in cross-section the impression is given 
that this mass is a symmetrical laccolith either within the Dead- 
wood formation or between the Deadwood and the underlying 
schists. The cross-section especially suggests that the sedimentary 
tT. A. Jaggar, Jr., “The Laccoliths of the Black Hills,’ Twenty-first Ann. Rept. 
U.S. Geol. Survey, Pt. 3 (1901), p. 242. 
