ABSTRACTS 411 



dislocations producing overthrust faults have occurred along several of 

 the veins. In the Grass Valley district there is one system with a 

 west-northwesterly direction and a steep northerly or southerly dip. 

 On this system the celebrated Idaho mine is located. Most of the 

 veins in the central and southerlv part of the district have a northerly 

 direction and a flat easterly or westerly dip. The veins are often 

 accompanied by strongly developed sheeting of the country rock. 



United States Geologic Atlas, Folio 28, Piedmont, West Virginia — 

 Maryland, i8q6. 



This folio consists of six pages of text, signed by N. H. Darton 

 and Joseph A. Taff, geologists, and closing with a series of vertical 

 sections showing the positions and thickness of the coal beds ; a 

 topographic map ; a sheet showing the areal geology of the district ; 

 another showing the economic geology ; a third exhibiting structure 

 sections; and a fourth containing a columnar section and a key to 

 the synonymy of the various formation names. The maps are on a 

 scale of 1 : 125,000. 



The area represented is about 925 square miles. In Maryland it 

 comprises the southern portion of Garret county and a small area in 

 the southwestern corner of Alleghany county. In West Virginia it 

 includes nearly all of Grant county, the western portions of Hardy and 

 Mineral counties, the northeastern portion of Tucker county, and a 

 narrow area of Preston county adjacent to the Maryland boundary 

 line. Its southeastern corner is in a region of Appalachian ridges, 

 and it extends northwestward over the Alleghany Mountains and the 

 Upper Potomac coal basin to the headwaters of the Youghiogheny 

 River, a branch of the Monongahela River. 



The geologic formations comprise members ranging from the 

 sandstones in the middle of the Silurian to the Upper Coal Measures 

 of the Carboniferous. In the southeastern portion of the area there 

 are two sharp anticlinal uplifts which bring up the Silurian rocks in 

 two prominent mountains. New Creek Mountain and Patterson Creek 

 Mountain. To the westward lies the coal basin which extends from 

 the Alleghany front to the Backbone Mountain. Along its center is 

 cut the deep gorge of the north branch of the Potomac River. The 

 basin is a relatively shallow one, but it contains about 3000 feet of 

 Carboniferous deposits.. To the westward is the anticlinal region of 



