Geologic Sfrncture of the Blue Ridge. — KeitJi. 365 
erick limestone is also Cambrian. North and south from this sec- 
tion the limestone is soon covered b}' the Jura-Trias sandstones, 
and its contact with the sandstones is not of sufficient extent to be 
free from doul)t. As a corroboration of the sequence made out 
in other places it is good but not sufficient for independent proof. 
With the discovery of the sandy shales overlying the massive 
sandstone the sequence was established as follows: 
(1.) Ill III iiiniilril iiiid iiiiittled liiiu'.'itoiic, with thin beds of slaty 
limestone, sandy shale, sandy limestone, and limestone 
conglomerate, Cambrian fossils. 
(2.) Fine (/rained, irldfc ■'<((ndi<f(n)r,\\\th beds of sliale. Lower 
Cambrian fossils 250 feet 
(3.) G)-ay sandy nhalex, with beds of sandstone abundant near 
the middle. Scolithus and Lower Cambrian fossils. 1,200 to 1,500 ft 
(4.) M((s^ii'e ivhite sandstone, with bluish-black bands, felds- 
pathic and in places conglomeratic 1,000 to 1,200 ft 
(5.) Gray and black slaty shales to 400 ft 
(6.) Igneous rocks. 
With the above sequence it is necessary to assume several faults 
to account for the present attitudes of the rocks. The fine sand- 
stone only once dips under the limestone, and then for only half 
a mile; the massive sandstone rarely passes under the sandy shale; 
and the igneous rocks occasional!}' pass over the massive sand- 
stone. Thrust-faults, therefore, exist between the limestone and 
sandstone belts and l)etween the two sandstone belts, ])y which 
the anticlines have l)een broken and thrust up till only the sj'n- 
clines remain. The faults along these two lines reach over the 
whole extent of the Blue Ridge and South mountain that has been 
studied, and locally the sandstone is faulted under the igneous 
rocks. 
East of Front Royal the two faults run together, the sandstones 
disappear and the igneous rocks are faulted against the valley 
limestone. The limestone-sandstone, or western, fault, is made 
manifest in many places by breccias of sandstone with calcareous 
matter, notably northeast of Front Royal. The eastern or second 
main fault is for the most part inferred from the secjuence, occa- 
sionalh' from the areal distribution of the rocks, as at. Monterey 
and Front Royal. 
On Catoctin mountain the structure is much simpler. The ap- 
parent normal se((ueiice at Frederick is broken to the north and 
