886 



SCIENCE. 



[N. S. Vol. V. No. 127. 



only the summits of which reach the original 

 level of the plateau. 



The geologic structure of this region varies 

 as the topography varies. In the northern por- 

 tion the rocks are nearly horizontal, their 

 northwestward slope being rarely more than 

 200 feet per mile, whereas in the southern por- 

 tion the rocks have been highly compressed in 

 a horizontal direction, forming huge folds, 

 which in many places have broken, allowing 

 one portion of the fold to slip over the other. 

 It is this tilted condition of the strata which 

 gives rise to the regular topographic forms of 

 the Appalachian valley. The attitude of the 

 rocks is shown on the structure-section sheet by 

 four sections which cross various portions of 

 the territory. 



The geologic history of this region is recorded 

 in the rocks, which tell of prevailing marine 

 conditions from early Cambrian to late Car- 

 boniferous time. There were deposited during 

 that time sediments to the extent of 17,000 or 

 18,000 feet in thickness, which have since been 

 hardened into limestone, shale and sandstone. 

 Of this great mass the limestones form about 

 6,700 feet ; the shales, 9,500 feet, and the sand- 

 stones, about 1,400. On lithologic grounds 

 these have been divided into twenty-three 

 separate and distinct formations, which are 

 shown on the general geologic map by various 

 colors and patterns. 



There is little variety in the mineral resources 

 of this region. Coal, iron ore and marble con- 

 stitute about all of the mineral wealth of the 

 territory. A limited area of coarse gray marble 

 occurs along the northern front of Big Walker 

 Mountain, but no development has been under- 

 taken. 



Iron ore occurs in two formations of the 

 Upper Silurian rocks. It is of good quality, 

 a;nd probably in sufficient quantity to be of com- 

 mercial importance, but its inaccessibility has 

 prevented development. 



Coal is by far the most important mineral re- 

 source of this region. The territory represented 

 by this sheet embraces almost the entire Flat 

 Top or Pocahontas coal field at present de- 

 veloped. All operations are confined to the 

 great No. III. or Pocahontas seam of coal, which 

 is semi-bituminous and ranges in thickness from 



4 to 10 feet. It is exposed along the valley of 

 Bluestone river from Pocahontas to the edge of 

 the territory, along Tug Fork, in the valley of 

 Elkhorn creek, from Coaldale to Kimball, near 

 the edge of the area and at several places on 

 the head streams of Guyandotte river. Mining 

 is restricted to the Bluestone region and the val- 

 ley of Elkhorn creek. In these two areas there 

 are at present in operation thirty-seven distinct 

 mines, which in 1894 produced 3,096,867 long 

 tons of coal. 



Folio 38, Piedmont, WestVirginia-Maryland, 1896. 



This folio consists of six pages of text, signed 

 by N. H. Darton and Joseph A. TaiT, geologists, 

 and closing with a series of vertical sections 

 showing the positions and thicknesses of the coal 

 beds ; a topographic map ; a sheet showing the 

 areal geology of the district ; another showing 

 the economic geology ; a third exhibiting struc- 

 ture sections, and a fourth containing a columnar 

 section and a key to the synonymy of the vari- 

 ous 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 Garrett county and a small area in 

 the southwestern corner of Allegany county. 

 In West Virginia it includes nearly all of Grant 

 county, the western portions of Hardy and Min- 

 eral counties, the northeastern portion of Tucker 

 county, and a narrow area of Preston county, ad- 

 jacent to the Maryland boundary line. Its south- 

 eastern corner is in a region of Appalachian 

 ridges, and it extends northwestward over the 

 Allegheny Mountains and the upper Potomac 

 coal basin to the headwaters of the Youghio- 

 gheny 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 Car- 

 boniferous. 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 Allegheny front to 

 the Backbone Blountain. Along its center is cut 

 the deep gorge of the north branch of the Po- 

 tomac river. The basin is a relatively shallow 



