No. 374.] REVIEWS OF RECENT LITERATURE. 139 
porphyry also occur in the district, but in small quantity only. All 
the basalts contain orthoclase in fairly large quantity. An analysis 
of the rock from a dyke at Valmont gives : 
SiO, TiO, Al,O; FeO, FeO CaO BaO MgO K,O Na,O P,O; Cl SO; H,O Total 
43.25, .89. 36.73: 3.99: 6.28 Bas .013" sI 4:08 piei O .12 1.72 =100,163 
The augite-syenite is a biotitic variety containing some bronzite. 
The tuffs occurring in the district are andesitic. These and cer- 
tain andesitic pebbles found in conglomerates are the only evidences 
met with in the study of the district that point to the former 
presence of andesite lavas in the vicinity. W.S.B. 
1 W. Cross, Ch. V. Geology of the Denver Basin in Colorado. Monograph 
XXVII. U.S. Geol. Survey, p. 315. 
