J. J. Stevenson—Faults of Southwest Virginia. 268 
and added greatly to the knowledgé of the general structure,* 
of which he first appears to have had a clear conception. Pro- 
fessor Safford’s map of Tennessee shows the extent of the 
faults in that State. The writer has made a reconnaissance of 
the faulted region in Virginia from the Tennessee line to almost 
twenty miles beyond New River, a distance of 150 miles, and 
has given the results in several memoirs read before the Ameri- 
ean Philosophical Society.t As these last are independent, 
information respecting the several faults is broken in such a 
way that a summary statement is necessary to render it avail- 
able. If more of detail should be needed, the reader is re- 
ferred to the memoirs cited. 
The “Great Valley” follows the northerly or northwesterly 
foot of the Blue Ridge from New England to Alabama and, 
except where broken by faults, is underlaid by Lower Silurian 
and Cambrian rocks. In New York, Pennsylvania and Mary- 
land, it is bounded on the northerly side by anticlinals and 
synclinals carrying the newer rocks so that within a little dis- 
tance oneis in the Upper Devonian. The conditions are simple, 
there being no faults of great longitudinal extent cutting off 
the valley on that side. The only faults lie at a considerable 
distance beyond the valley and, though of much interest, are 
utterly insignificant in comparison with those found farther 
south. 
At no great distance southward in Virginia, strips of Lower 
Silurian are shown beyond the line of the “Great Valley.” 
These are more numerous near New River and become wider 
thence to the Tennessee line; while near and beyond the same 
river the valley itself is broken by patches of Upper Silurian, 
Devonian and even Lower Carboniferous rocks. These great 
changes are due to faults as remarkable for their longitudinal 
as for their vertical extent. 
The greatest width of the faulted area in southwest Virginia 
is about forty miles, measured along a line passing through 
Wythe, Giles and Tazewell Counties of Virginia. The faults, 
separated by varying intervals, show Knox limestone on the 
southerly or upthrow side, while the beds on the northerly or 
downthrow side may belong anywhere from Lower Silurian to 
Upper Carboniferous. Thus the region is broken into a series 
of alternating “rich” and “poor” valleys, underlaid in the 
former by Lower Silurian limestones and in the latter by 
Upper Silurian and Devonian shales. The sections shown by 
* Professor Lesley’s papers were read before the American Philosophical 
Society on May 16th, 1862, and on April 21st, 1871. 
+ The dates of these papers are August 20th, 1880; January 21st, 1881, Octo- 
ber 7th, 1881, November 21st, 1884, and one not yet read before the Society. 
Am. Jour. Scl.— THIRD SuRIEs, VoL. XX XIII, No. 196.—APpRiL, 1887. 
17 
