Decembke 13, 1895.] 



SCIENCE. 



789 



of this territory, both in the form of limo- 

 nite and in that of hematite. Red fossil 

 ore is found in the Eockwood formation in 

 the northern part of the region, and it is 

 mined on Wallen Eidge, south of Big Stone 

 Gap. Coal is the principal mineral re- 

 source of this territory. It occurs in the 

 structural basin north of Stone Mountain, 

 and sparingly in the great arch of Powell 

 Mountain, east of High Knob. The coal- 

 bearing rocks are appi-oximately 5,000 feet 

 in thickness and include many seams of 

 "workable coal. In the vicinity of Big Stone 

 Gap the Imboden seam is the most impor- 

 tant. It has been traced over a large area 

 on the Virginia side of the basin, where it 

 varies ii-om 3 to 16 feet in thickness. On 

 this side there are a number of other seams 

 of good quality, ranging from 3 to 7 feet in 

 thickness, which could be easily worked. 

 The Kentucky portion has also many work- 

 able seams, but at present, owing to lack of 

 transportation, no mining has been done on 

 a commercial scale. 



FOLIO 13, FEEDEBICKSBTJEG, VIEGINIA-MAEY- 

 LAND, 1894. 



This folio consists of 5\ pages of text, 

 signed by N. H. Darton, geologist, and W 

 J McGee, geologist in charge ; a topo- 

 graphic map of the district (scale 1:125,000), 

 and a sheet showing the areal geolog}^ 



The map represents an area of approxi- 

 mately 1,000 square miles of the Coastal 

 Plain region of northeastern Virginia and 

 the southwestern corner of Charles county, 

 Maryland. It includes, in Virginia, King 

 George and the greater part of Caroline and 

 Stafford counties and adjoining portions of 

 Spottsylvania, Essex and "Westmoreland 

 counties. The city of Fredericksbui'g is 

 near the center of the western margin of 

 the area. The Potomac Eiver crosses the 

 northeastern corner of the area, and the 

 Eappahannock Eiver extends diagonally 

 across its center on a northwest and south- 



east line. The headwaters of the Mattapony 

 Eiver are in its southwestern corner. Along 

 these river valleys there are wide, low ter- 

 races capped by the Columbia formation, of 

 Pleistocene age. The intervening areas are 

 plateau remnants capped by Lafayette de- 

 posits, of supposed Pliocene age. The 

 underlying formations are the Potomac, 

 Pamunkey and Chesapeake, which lie on 

 an east-sloping floor of crystalline rocks. 

 This floor rises to the surface and consti- 

 tutes hills of considerable height in the 

 northwestern corner of the tract ; eastward 

 it is deeply buried under the Mesozoic and 

 Tertiary sediments. The Potomac forma- 

 tion, which is the basal member of these 

 sediments, consists of a heterogeneous 

 series of sands and sandstones with interca- 

 lated claj's. Much of the sand is arkosic, 

 and consists of detritus of crystalline rocks. 

 The Pamunkey formation, which overlies 

 the Potomac unconformably, is the repre- 

 sentative of the Eocene in this region. It 

 consists in greater part of glauconitic marls. 

 These marls are important fertilizers, and 

 in some porttons of the region have been 

 used with excellent results. They are over- 

 lain unconformably by the Chesapeake for- 

 mation, which is of Miocene age. It is 

 characterized by fine sands, marls and clays, 

 portions of which consist largely of diatom 

 remains. It is the same series that extends 

 to Richmond, where its diatomaceous char- 

 acter was discovered many years ago, and 

 to the northward through Maryland. It 

 thickens rapidly eastward, and is nearly 

 1,000 feet thick in the lower Chesapeake 

 Bay district. 



The crystalline rocks consist mainly of 

 granites and gneiss and an infolded belt of 

 slates, to which the name Quantico slates 

 has been given. They are not of value for 

 roofing slates, so far as is now known. They 

 appear to be a continuation of the slates in 

 the belts west of Eichmond in which lower 

 Silurian fossils were discovered some time 



