362 TJ(e American Geologist. DcnHibwr, i8fl2 
sion of Ihc hind on whicli it hiy, ;iii(l to liuvc witnessed, during 
tiu> retreat and removal of its load, a progressive re-elevation of 
the same area to its present higlit. 
For Europe, also, after reading the recent very ably written 
article l)y Prof. James Geikie."" in which he argues for five dis- 
tinct epochs for glaciation, 1 think that there, as here, it is more 
reasonable to refer th(> whole of tlie glacial drift to a single glacial 
epoch, with moderate fluctuations in the extent of the ice-sheets and 
glaciers. In thus ditferiug from this eminent glacialist and from 
Wahnschatl'e in (irermany, Penck in Austria, and DeGeer in 
Sweden, who aiv of the same opinion with Geikie, that there were 
lono- mild interglacial epochs in Europe, \ come into agreement, 
on this ([uestion, with other distinguished European glacialists, 
as Lamplugh in England, Falsan in France, and Hoist in Sweden, 
who hold that the Quaternary reign of ice was essentially a unit. 
But this present state of our division under the two opinions surely 
calls for much further observation and candid study that ulti- 
mately the truth may be confidently known, on whichever side 
it may be. 
THE GEOLOGIC STRUCTURE OF THE BLUE RIDGE 
IN MARYLAND AND VIRGINIA. 
V>\ AuTiiru Keith, of thf I'. S. Geologiciil Survi'v, \\'asliingtoii, 1). C. 
In the following pages there will be discussed the belt of rocks 
in Virginia and Maryland, lying between the Shenandoah and 
Cuml»erland valleys and the Piedmont plain. Attention will 
be given chiefly to their structural relations as they have been 
brought out by recent discoveries of fossils. The topographic 
features of the belt are in brief (1) the great limestone valley on the 
west, (2) the Jura-Trias plain on the east, and (3) between them 
the mountain belt which consists of the South Mt. -Blue Ridge 
chain and Catoctin-Bull Run Mt. chain enclosing a broad level 
valley. The topography is the direct result of difterential erosion 
among hard and soft rocks, and accordingly is a key to their areal 
distribution. The mountains are formed l)y sandstones and the 
intermediate valley by granites and schists. In passing north- 
ward through Maryland the granite areas rapidly lessen and dis- 
appear, and the valley contracts to insignificant dimensions. 
•""On the Glacial Succession in Europe." Trans., lioyal Society of 
Edinburfrh, Vol. \\\vti. jiji. 127-149, with niap. May. 1892. 
