AUTHORS’ ABSTRACTS. 973 
east-sloping floor of crystalline rocks. This floor rises to the surface 
and constitutes hills of considerable height in the northwestern corner 
of the tract; eastward it is deeply buried under the Mesozoic and 
Tertiary sediments. The Potomac formation, which is the basal member 
of these sediments, consists of a heterogeneous series of sands and 
sandstones with intercalated clays. Much of the sand is arkosic, and 
consists of detritus of crystalline rocks. The Pamunkey formation, 
which overlies the Potomac unconformably, is the representative of 
the Eocene in this region. It consists in greater part of glauconitic 
marls. These marls are important fertilizers, and in some portions of 
the region have been used with excellent results. They are overlain 
unconformably by the Chesapeake formation, which is of Miocene 
age. It is characterized by fine sands, marls, and clays, portions of 
which consist largely of diatom remains. It is the same series that 
extends to Richmond, where its diatomaceous character was discovered 
many years ago, and to the northward through Maryland. It thickens 
rapidly eastward, and is nearly 1000 feet thick in the lower Chesapeake 
Bay district. 
The crystalline rocks consist mainly of granites and gneiss and an 
infolded bed of slates, to which the name Quantico slates has been 
given. They are not of value for roofing slates, so far as is now 
known. They appear to be a continuation of the slates in the belts 
west of Richmond, in which lower Silurian fossils were discovered 
some time ago, but no fossils have been found in the area of the 
Fredericksburg sheet. 
U.S. Geologic Atlas, Folio 14, Staunton, Virginia, West Virginia, 1894. 
This folio consists of four pages of text, signed by N. H. Darton, 
geologist, and closing with a columnar section of the area; a topo- 
graphic map (scale 1: 125,000), a sheet showing the areal geology of 
the district, another showing the economic geology, and a third 
exhibiting structure sections. 
The area represented is about tooo square miles of central 
Appalachian Virginia. It comprises central and western Augusta 
county and portions of several adjacent counties. Staunton lies near 
the center of the eastern margin of the tract. About a third of the 
area is in the Great Valley of Virginia, and the remainder stretches 
halfway across to the Allegheny. 
The geologic formations comprise members from the Shenandoah 
