REVIEWS 181 



svnclinorium. The relations of the granite and quartz-diorite to the sediments are 

 not definitely known, but their distribution is such as to suggest that they are intrusive 

 into the hornblende schists at the base of the sedimentary series, and that with the horn- 

 blende schists they form the basement upon which the sedimentary rocks were deposited. 

 The gabbro is intrusive into the sediments. 



Comment. — The description indicates that the basal rock of this region, the horn- 

 blende schist, is similar in essential features to the schistose volcanic rocks with asso- 

 ciated sediments making up the Keewatin series, the lowest in the Lake Superior region. 

 Waldemar Lindgren. "A Geological Reconnaissance Across the Bitterroot 

 Range and Clearwater Mountains in Montana and Idaho." Professional 

 Paper No. 27, U. S. Geological Survey, 1904. With geological map. 

 Lindgren makes a geological reconnaissance across the Bitterroot Range and 

 Clearwater Mountains in Montana and Idaho. Practically the entire area of the 

 Bitterroot and Clearwater Mountains is occupied by granite with some gneiss. West 

 of the Clearwater River, and only imperfectly exposed below the lava, is an extensive 

 sedimentary area adjoining this granite; smaller sedimentary areas are exposed on Lolo 

 Fork and on the head of the South Fork of Bitterroot River. In no place have well- 

 defined fossils been found, but there is some foundation for the belief that the two last- 

 named areas on the east side are very old, possibly pre-Cambrian, while the western 

 area probably includes Triassic, Carboniferous, and possibly still older sediments. 

 The granite constitutes a great bathylith whose age is not certain, but probably of post- 

 Triassic age. The gneisses include older gneisses of the Clearwater Mountains, prob- 

 ably of pre-Cambrian age, and later gneisses resulting from the deformation of the 

 granite occurring principally on the eastern side of the Bitterroot Mountains. On the 

 accompanying map all are colored together as pre-Tertiary. 



F. L. Ransome. "The Geology and Ore Deposits of the Bisbee Quadrangle " 

 Professional Paper No. 21, U. S. Geological Survey, 1904. "Geology of the 

 Globe Copper District, Arizona." Professional Paper No. 12, U. S. Geo- 

 logical Survey, 1903. "Description of the Globe Quadrangle." Geologic 

 Atlas of the United States, Folio No. in, 1904. "Description of the 

 Bisbee Quadrangle." Geologic Atlas of the United States, Folio No. 112, 

 1904. 



Ransome describes in the Pinal Mountains of the Globe district of Arizona mica- 

 schists with occasional bands of amphibole-schists which he calls the Pinal schists. 

 These are intruded by quartz, mica-diorite, and granite. The schists and intrusives 

 are unconformably below a non-fossiliferous series supposedly of pre-Cambrian age. 

 The schists are believed to represent metamorphosed arkoses or grits. They are 

 probably to be correlated with the Vishnu series of the Grand Canyon, provisionally 

 called Algonkian by Walcott. In the absence of other criteria the Pinal schists are 

 referred to the pre-Cambrian. 



In the Mule Mountains of the Bisbee district, 90 miles to the south, are similar 

 schists, also called Pinal schists. 1 Evidence of sedimentary origin is less satisfactory 

 then in the Globe district and pre-Cambrian granitic intrusives are absent. Here also 

 they are referred to the pre-Cambrian. 



1 The Pinal schists probably correspond to the Arizonian schists of Blake, Engi- 

 neering and Mining Journal, Vol. XXXV (1883), pp. 238, 239. 



