x.l MARYLAND. 
DESCRIPTION. 
187 
The Greenbrier formation,, where best developed in Maryland, con- 
sists of three distinct members. The lowest is a series of limestones, 
usually siliceous near the base, and varying from 27 to 46 feet in thick- 
ness. The middle member consists largely of shales, thin sandstones, 
etc., and varies from 88 to 98 feet in thickness. The upper member 
consists almost entirely of veiy pure limestones, and is from 65 to 85 
feet thick. 
The section below, quoted from the Garrett County report of (he 
Maryland Geological Survey, will serve to illustrate the characters of 
the various members of the Greenbrier formation. 
Section of Greenbrier formation at Crabtree, Garrett County. 
Upper member: Feet. 
Argillaceous limestone 4 \ 
Massive sandy limestone 13 
Red sandy limestone 2 
Gray limestone . 3 
Red calcareous shale 3h 
Red sandy limestone 8 
Gray sandy limestone with red bands 21 
Gray limestone 10 
65 
iMiddle member: 
Red shale, with thin bands of gray sandstone SO 
Pure white sandstone 8 
Lower member: 
Gray limestone. 
ss 
COMPOSITION. 
The upper member of the Greenbrier formation consists very largely 
of thick beds of pure' limestone. These limestones have been very 
extensively used for flux and for lime burning, and their range in 
composition is fairly well established. 
The series of analyses given below is representative of these upper 
limestones. They are commonly very low in magnesium carbonate, 
though occasional beds will show a prohibitive percentage of that 
ingredient. In places they carry sufficient silica, alumina, and iron 
oxide to approximate to the composition of the Lehigh cement rock, 
but usually it will be necessary to add a considerable proportion of 
clay or shale in order to bring the mixture up to correct composition 
for Portland cement. 
