November 29, 1895.] 



SCIENCE. 



715 



Park about the middle of the southern 

 border, flows northwest and north through 

 a closed valley 30 miles long and three 

 miles wide, and at Livingston turns north- 

 east and enters the broad open valley be- 

 yond the frontal ranges of the Eocky Moun- 

 tains. 



The rocks forming the surface of the 

 country are partly crystalline schists, in- 

 cluding gneiss, schists, with granite and 

 other granular rocks ; partly sedimentary 

 formations, including limestone, sandstone 

 and shales ; and partly lavas and other 

 igneous rocks. The crystalline schists are 

 mainly Archean and constitute a large ]3art 

 of the southern half of the region. They 

 form the higher mountains and plateau 

 drained by Boulder Eiver and those from 

 Emigrant Peak south. A small area of 

 sandstones, conglomerates, slates and arena- 

 ceous limestones occurring in the Bridger 

 Eange have been referred to the Algonkian. 

 They lie unconformably upon the crystal- 

 line schists, and are overlain unconformably 

 by the Paleozoic series. 



The sedimentary formations cover one- 

 half the area, and present a total thickness 

 of 20,000 feet, embracing all the grand di- 

 visions of geologic time since the Archean. 

 The chief feature is the great development 

 of the latest Cretaceous strata, which are 

 12,000 feet thick above the Laramie, the 

 total thickness of the Paleozoic being only 

 3,500 feet. The series from the basal (Flat- 

 head) quartzite to and including the Lara- 

 mie coal beds is conformable throughout. 

 The Paleozoic strata occur upturned at 

 steep angles against the crystalline schists 

 or in steep anticlines. The lowest bed is 

 the Flathead quartzite. Above it are 

 shales and limestones of Cambrian age. 

 The Silurian is represented by only a few 

 feet of formation, whose precise age is 

 doubtful. Four hundred and fifty feet of 

 shales and limestones represent the Devo- 

 nian. The Carboniferous strata are 2,000 



feet thick. They are here, as elsewhere, 

 the mountain limestones and form the crest 

 of the Bridger Eange and the summits of 

 some peaks of the Snowy Eange. The 

 Trias is recognized only in the southern 

 part of the region, as thin belts of red 

 sandstone. The Jura varies considerably 

 in character, being mostly shales and fis- 

 sile limestones. These two formations are 

 500 feet thick. 



The Cretaceous constitutes more than 

 one-half of the total thickness of strata. 

 Its lowest member is the Dakota conglom- 

 erate with sandstone and some shale. Over 

 this is the Colorado group, including Ben- 

 ton shales and ISTiobrara limestone, aggre- 

 gating 1,800 feet in thickness. Over this is 

 the Montana group, 1,800 feet thick, con- 

 sisting of Pierre shales and Fox Hills lime- 

 stones. The Laramie sandstone, with some 

 intercalated clays and beds of coal, is 1,000 

 feet thick. Above this is a slight uncon- 

 formity, followed by conglomerates, sand- 

 stones and clays of the Livingston forma- 

 tion 12,000 feet thick. Near the base 

 the conglomerate consists largely of vol- 

 canic material. True tuff-breccia of vol- 

 canic rocks occurs intercalated near the 

 base of the series on Boulder Eiver. 



ISTeocene lake beds occur in Gallatin Val- 

 ley, and on Yellowstone Eiver opposite 

 Fridley. 



Surficial deposits of the Pleistocene pe- 

 riod occur as alhivium over all the broader 

 river vallej'S. Glacial drift, consisting of 

 gravel, sand and boulders, is scattered over 

 the higher parts of the country and covers 

 the Yellowstone Valley south of Chicory. 



Igneous rocks occupy a large part of 

 the area of this sheet. They consist of 

 subaerial breccias or agglomerates with 

 tuffs and lava flows and of intrusive bodies, 

 such as dikes, sheets, laccolites and stocks 

 or necks. They occur extensively in the 

 southeastern corner of the district and 

 form the Gallatin Eange along the south- 



