3L.1 VIRGINIA. 313 
) similar work in the southern half of the Valley of Virginia. The 
blowing preliminary report is \)iisvd largely upon this later held 
ork, but in its preparation free use has been made of the Staunton 
olio" by N. H. Darton, and of an article by Charles Catlett, entitled 
Cement Resources of the Valley of Virginia." 6 Acknowledgments 
re also due to Prof. H. D. Campbell, of Washington and Lee Uni- 
ersity, for the use of manuscript geologic maps prepared by him, 
Dvering the region about Lexington and Natural Bridge, Va. Mr. 
atlett has also kindly allowed the writer to make use of notes and 
reliminary analyses made by him of the rocks in the vicinity of 
[arrisonburg and Staunton, Va. 
A somewhat more detailed report, with maps, by the present writer, 
ill be found in Bulletin U. S. Geol. Survey No. 260. During the 
ason of 1905 further investigations will be made in the field, in 
aoperation with the Virginia Geological Survey, and a complete 
rport on the cement resources of Virginia will be published at the 
ose of this held work. 
In the present report only that part of the valley lying between 
Woodstock, in Shenandoah County, on the north, and Natural Bridge, 
i Rockbridge County, on the south, is considered. 
The raw materials occurring in the valle}^ of Virginia that are suit- 
ble for the manufacture of cement are argillaceous limestones, pure 
mestones, shales, and calcareous marls. Of these the more impor- 
int are the argillaceous and pure limestones. 
The principal rock formations in the Valley of Virginia are a great 
jries of limestones termed the Shenandoah limestone and a series of 
mles named the Martinsburg shales. In general the entire valle} 7 is 
nderlain by the Shenandoah limestone, while the shales usually out- 
op along the base of the mountains bounding it. Both of these 
jrmations yield an abundance of the raw materials required in the 
anufacture of Portland cement. 
SHENANDOAH LIMESTONE. 
This is a very great, thick formation, composed of several members, 
'he chemical composition of its several divisions varies greatly. Some 
f the limestones are highly magnesian; others are almost pure cal- 
ium carbonate; while one group contains a considerable amount of 
layey material. In the Shenandoah limestone four divisions may be 
ecognized, based on character of the rock and its fossils. These, 
amed in ascending order, are as follows: (1) A series of dolomitic 
mestones from 1,000 to 2,000 feet thick, of Cambrian age; (2) 300 or 
lore feet of cherty limestone bearing fossils of Beekmantown (Cal- 
if erous) age; (3) 60 to 100 feet of a coarsely crystalline light-colored 
ighly fossilifcrous limestone, and (4) 200 to 350 feet of dark-colored 
"Geologic Atlas, U. S., folio 14, U. S. Geol. Survey, 1894. 
&Bull. U. S. Geol. Survey No. 225, 1904, pp. 157 161. 
