(r6()l'>gic Sfrnrtiire of t lie Blni; Ridge. — Keith. '3(>^ 
South Mt. find Blue Ridge have been the subjects of numerous 
discussions in previous years, and publications concerning them 
have been made Ijy llogers Bros., Hunt. Fontaine. Leslie, Frazer 
and Greiger and lv<^ith. All of these discussions have been based 
on physical evidence alone and have scarcely brought out the com- 
plexity of the chain. 
In isni Lower Cam1)rian fossils were found in the Blue Ridge 
at Balcony Falls, Va., by Walcott, and in August. 1892, he found 
Lower Cambrian fossils at Mt. Holly at the north end of South 
mountain and in the rocks of York valley, in Pennsyhania. In 
the latter end of August the writer accompanied Walcott through 
the mountani belt in Maryland and Pennsylvania with the purpose 
of finding fossils, and establishing the age of the entire chain. 
Search was directed especially to the sandstones and shales form- 
ing the mountain ranges and was abundantly rewardeil. One layer 
in particular, the topmost one. yielded fossils in greatest abund- 
ance wherever tested. (The fossils will be descriljed by 3Ir. AVal- 
cott in the American Journal of Science for December.) Subse- 
quently the structure of the mountain belt was worked l)y the 
wi'iter in this new light, from the Pennsylvania line southward tO' 
Thoroughfare Gap in Bull Run mountain and Front Royal along 
the Blue Ridge. Lower Caml)rian fossils were found as far south 
as Manassas (lap in the Blue Ridge. 
The rocks of the mountain l)elt fall into \\\o classes, sediment- 
ary and igneous, each with several divisions. The igneous rocks 
will be full}' descril)ed in Am. J. Science for December, by Prof. 
G. H. Williams, and only briefly touched upon here. 
Bro.xdly considered, the region is a In'oad anticline and succes- 
sivel}' younger rocks appear east and west fn^m the nucleus of 
igneous rocks. This arch is crumpled into several synclines and 
broken l>y faults that follow the mountain lines quite closely. 
The resultant structure is (piite complicated, and therc' are very 
few places in which a normal and complete section can be found. 
Five t^pes of sedimentary rock occur: (1) the Siluro-Caml»rian 
limestone of the great valley. (2) fine calcareous white sandstone. 
(8) greenish gray sandy shales with thin sandstone l»eds, (4) mass- 
ive white sandstone in places conglomeratic with streaks and 
bands of black, (o) shale, usuall}^ black and slaty. As pointed 
out 1)V Geiger and Keith, these types occur in distinct bands fol- 
lowing the lines of structure. The tine s:nidst<>ne caps a line of 
