180 REVIEWS 



a rudely triangular area twenty miles in length and ten miles wide in its widest part, 

 near the western end. The porphyry and aporhyolite areas occur in the Arbuckle 

 Mountains proper in the western end of the uplift. 



In the Wichita Mountains pre-Cambrian granite, granite-porphyry, and gabbro 

 cut by diabase form a considerable part of the mountains. Granite is the principal 

 mountain-making rock in the Wichita region. Its area is greater than that of all the 

 other igneous rocks combined, and is about equal to that of the others and the older 

 Paleozoic sediments. It makes all of the high land of the Wichita, Quana, Devil's 

 Canyon, and Headquarters Mountains, and a large part of the Raggedy group. 



The gabbro is exposed for the most part in the valleys or on the plains which sur- 

 round the mountains. The granite porphyry comprises practically all of the Carlton 

 Mountains, the igneous mass lying between the limestone hills in the vicinity of Blue 

 Canyon, north of Mount Scott, and some hills near the northwest end of the limestone 

 areas east of Rainy Mountain Mission. 



Ernest Howe. "An Occurrence of Greenstone Schists in the San Juan Moun- 

 tains, Colorado." Journal of Geology, Vol. XII (1904), pp. 501-9. 

 Howe describes green schists in the pre-Cambrian of the Needle Mountains in 

 San Juan and La Plata Counties of southwestern Colorado. They comprise massive 

 and schistose, granular and porphyritic meta-gabbro, and areas of mashed granitic 

 intrusives and other schistose rocks, presumably altered quartzites. No evidence of 

 surface origin is noted in the igneous rocks. The greenstones antedate the Algonkian 

 sediments to the north, as shown by the pebbles contained in the Algonkian conglomer- 

 ate, and have an older aspect than the other rocks of the neighboring areas. They 

 are therefore assigned to the early Algonkian. Attention is called to their similarity 

 to the greenstones of the Menominee and Marquette districts of Michigan and to rocks 

 near Salida, Colo. 



Arthur C. Spencer. "The Copper Deposits of the Encampment District, 

 Wyoming." Professional Paper No. 25, U. S. Geological Survey, 1904. 

 Spencer discusses the geology of the Encampment district of Wyoming. Pre- 

 Cambrian rocks form the main mass of the Sierra Madre Mountains with Mesozoic 

 beds dipping away from them. They comprise sedimentary and igneous rocks. The 

 sedimentary rocks are from the base up: hornblende schists, derived from surface 

 volcanic rocks, interbedded with thin but persistent beds of sandy shale and impure 

 limestone, limestone, quartzite, slate, and conglomerate. In the Encampment area the 

 quartzite and slate formation is more in evidence than any other of the bedded rocks, 

 but all occur in a limited area having the form of a narrow triangle, with its apex on the 

 Encampment River about 5 miles south of Encampment, and its base, about 7 miles 

 wide, in the foothills on the west side of the range. The belt of quartzites and asso- 

 ciated strata is exposed for about 20 miles, but on the west their extent is not known, 

 since they are overlapped by younger formations. The rocks within the sedimentary 

 belt strike in general nearly east and west, and they seem at first sight to have an 

 enormous thickness, since they dip almost invariably toward the south. An examina- 

 tion shows the sediments to be in an east-and-west synclinorium with axial planes of 

 both major and minor folds dipping to the south. Strike faults and transverse faults 

 are common. 



A complex of igneous rocks comprising granite, quartz diorite, and gabbro, occur 

 both to the north and south of the synclinorium, and the gabbro occurs also within the 



