972 THE JOURNAL OF GEOLOGY. 
The mineral resources of this region are important, though at 
present but slightly developed. A belt of marble, varying consider- 
ably in composition and appearance, outcrops along the northern side 
of Clinch Mountain. Iron ore occurs in many parts of this territory, 
both in the form of limonite and in that of hematite. Red fossil ore 
is found in the Rockwood formation in the northern part of the region, 
and it is mined on Wallen Ridge south of Big Stone Gap. Coal is 
the principal mineral resource 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 approximately 5000 feet in thickness, and include many seams of 
workable coal. In the vicinity of Big Stone Gap the _ Imboden seam 
is the most important. It has been traced over a large area on the 
Virginia side of the basin, where it varies from 3 to 16 feet in thick- 
ness. On this side there are a number of other seains of good quality, 
ranging from 3 to 7 feet in thickness, which could be easily worked. 
The Kentucky portion has also many workable seams, but at present, 
owing to lack of transportation, no mining has been done on a com- 
mercial scale. 
U.S. Geologic Atlas, Folio 13, Fredericksburg, Virginia; Maryland, 1804. 
This folio consists of five and one-fourth pages of text, signed 
by N. H. Darton, geologist, and M. J. McGee, geologist in charge; 
a topographic map of the district (scale 1: 125,000), and a sheet 
showing the areal geology. 
The map represents an area of approximately 1ooo square miles 
of the Coastal Plain region of northeastern Virginia and the south- 
western 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. Thecity of Fredericksburg is near the center of the western 
margin of the area. The Potomac River crosses the northeastern corner 
of the area, and the Rappahannock River extends diagonally across its 
center on a northwest and southeast line. The headwaters of the 
Mattapony River are in its southwestern corner. Along these river 
valleys there are wide, low terraces capped by the Columbia formation, 
of Pleistoceneage. The intervening areas are plateau remnants capped 
by Lafayette deposits, of supposed Plioceneage. The underlying for- 
mations are the Potomac, Pamunkey, and Chesapeake, which lie on an 
