12 The American Geologist. juiy, 1892 
selected somcwliat tirbitrarily und applied to beds in most eases 
comprising a much greater stratigraphic range than the name im- 
plies, including deposits having coiUxlinate names in New York, 
but not presenting typical characters in Virginia. The system 
of classification and nomenclature by which 1 was guided in 
mapping the formations in central Appalachian Virginia is the one 
adopted by the U. S. Geological Survey and described in the 
Tenth Annual Report of the Director, pages 56 to 79. The fol- 
lowing quotations from this report are given in explanation: 
'•The structural divisions shall be the units of cartography and shall 
be designated /o?■^^^a/^■oH 8. Their discrimination shall be based upon the 
local sequence of rocks, lines of separation being drawn at points in 
the stratigraphic column where lithologic characters change. * * * 
In every case the definition should be that which best meets the prac- 
tical requirements of the geologist in the held and the prospective 
user of the map; that is to say, each formation should possess such 
characteristics that it may be recognized on the ground alike by the 
geologist and by the layman. 
' "As each lithologic unit is the result of conditions of deposition that 
were local as well as temporary, it is to be assumed that each formation 
is limited in horizontal extent; the formation should be recognized and 
should be called by the same name as far as it can be traced and identi- 
fied by means of its lithologic characters, aided by its stratigraphic 
associations and its contained fossils. 
"The formations shall receive distinctive designations. The most de- 
sirable designations are binomial, the first member being geographic 
and the other lithologic. * * * When the formation consists of beds 
differing in lithologic character, so that no single lithologic term is ap- 
plicable, the word "formation" shall be substituted for the lithologic 
terra (e. g., Potomac Formation). 
"In the application of formation names, the laws of priority and pre- 
scription shall be observed; but in general the name previouslj" given 
to a structural unit of unlike definition shall not be given to the newly 
defined formation." 
As the Staunton sheet is to be the first published of the maps 
of Appalachian Virginia, it was necessary in its preparation to 
carefully consider a nomenclature for the stratigraphic units for 
the region, and to select names which involved no further cor- 
relation than was at present practicable. To this end a few 
names already known were adopted, together with several new 
names derived from prominent localities in the general region. 
These names are applicable for all of central Appalachian Vir- 
ginia, and in some cases for a wider area. They are given in the 
