November 29, 1895.] 



SCIENCE. 



quartzite, 50-300 feet thick ; the Benton 

 shale, 150-300 feet thick ; the Niobrara 

 limestone, 100-200 feet thick ; the Mon- 

 tana formation, comprising the Pierre 

 shales and Fox Hills sandstones, 600-2,000 

 feet thick ; the prevailing lithologic char- 

 acteristics of each of which are indicated by 

 its name. Among latei- beds are the Ohio 

 formation, about 200 feet of sandstones and 

 conglomerates, and the Euby formation, 

 with a maximum thickness of 2,500 feet of 

 sandstones, shales and conglomerates made 

 up to a large extent of eruptive debris. 

 These formations are separated by an un- 

 conformity from the underlying Laramie, 

 and to the west of this area pass beneath 

 the beds of the Wasatch Eocene ; in the 

 absence of fossil evidence they have been 

 classed as Cretaceous. 



The geologic structure of this region 

 affords evidence of no less than four imjjor- 

 tant orographic movements, involving the 

 making of new land, the erosion and plan- 

 ing down of the same and the inauguration 

 of a new cycle of sedimentation, which ac- 

 count for the great variation in thickness 

 of certain foi-mations. First, during Post- 

 Archean time, the first deposits, after which 

 were Upper Cambrian (Sawatch quartzite) ; 

 second, during Carboniferous time, followed 

 by deposition of Weber shales and Maroon 

 conglomerates; third, during Mesozoic time, 

 followed by deposition of the Gunnison 

 sandstone; and fourth, after Laramie time, 

 followed by the Ohio, Euby and Eocene 

 formations. 



Mineral Resources. — The most imj)ortant 

 economic product of the region is its coal, 

 which is found in the lower part of the Lai-a- 

 mie Cretaceous formation, between beds of 

 sandstone. The quality of the coal varies, 

 according to local conditions more or less 

 favorable to metamorphism, from dry bitu- 

 minous, through coking coal, to semi-an- 

 thracite and anthracite. Next in impor- 

 tance are its silver ores, which occur for the 



most part in true veins or fault fissures in 

 all varieties of rock, but mainly in the sedi- 

 mentary beds of upper horizons near erup- 

 tive rocks. The ores are generally rich, 

 but in small bodies, and, in consequence of 

 natural obstacles to cheap mining, have not 

 been extensively worked. Gold has been 

 found in paying quantities in the alluvium 

 of a single gulch; lead and copper are ac- 

 cessory products in limited amounts. 



FOLIO 10, HAEPEB's FEEEY, VIRGINIA, MAEY- 

 LAND, WEST VIEGINIA, 1S!)4. 



This folio consists of 4 pages of descrip- 

 tive text, signed by Arthur Keith, geolo- 

 gist; 1 page of columnar section, a topo- 

 graphic map (scale 1 :125,000) , a sheet show- 

 ing the area! geology of the district, an- 

 other showing the economic geologj^, and a 

 third exhibiting structure sections. 



The folio describes that portion of the 

 Appalachian province which is situated be- 

 tween parallels 39° and 39° 30' and merid- 

 ians 77° 30' and 78°. The tract contains 

 about 950 square miles and falls within 

 Washington and Frederick counties, Mary- 

 land ; Loudoun and Fauquier counties, Vir- 

 ginia ; and Jefferson county. West Virginia. 



The folio begins with a general descrip- 

 tion of the province, which shows the rela- 

 tion of the Harper's Ferry tract to the 

 whole. Then the local features of the 

 drainage by the Potomac and Shenandoah 

 rivers and their tributaries (Goose, Antie- 

 tam and Catoctin creeks) are treated. The 

 various forms of the surface are pointed 

 out, such as Shenandoah Vallej', Blue 

 Eidge and Catoctin Mountain, and their 

 relations to the underlying rocks are made 

 clear. 



Under the heading Stratigraphy the 

 geologic history of the Appalachian pro- 

 vince is presented in outline, and the local 

 rock groups are fully described in regard to 

 composition, thickness, location, varieties, 

 and mode of deposition. 



