MARYLAND. 179 
PORTLA^D-CKMElSrT RESOURCES OF MARYLAND. 
Up to the present time no Portland-cement plants have been built in 
laryland, but three limestone formations in the State are so well 
)eated and so satisfactory in chemical composition as to give promise 
f being future sources of supply of Portland-cement materials, 
everal other limestones occur, but are either too high in magnesia or 
therwise not well adapted to cement manufacture. The three avail- 
Die limestone formations above noted are, in descending order, as 
)llows: 
Name. 
Geologic age. 
reenbrier limestone 
Mississippian. 
Silurian. 
Ordovician (Lower Silurian). 
3\viston or Helderberg limestone 
-enton limestone 
The areal distribution of these three limestones in Maryland and 
e adjoining States is shown on the geologic map, PI. XV, opposite 
ige 314. 
TRENTON LIMESTONES AND ADJACENT CLAYS. 
DISTRIBUTION AND CHARACTER. 
The Cambro-Ordovician limestones, including the Trenton lime- 
one, which is the special object of interest here, occur in three prin- 
pal areas in Maryland, two of which are in Washington County and 
e in Frederick. 
The westernmost area enters Maryland from Pennsylvania in central 
ashington County, and runs in a direction slightly west of south to 
)tomac River, which it reaches between Cherry Run and Williams- 
rt. The eastern border of this limestone belt lies just west of Con- 
ocheague Creek, while Little Conococheague Creek lies in the lime- 
3ne area. Fairview, Reiffs, Hicksville, and Clear Spring are located 
the limestone. 
The central limestone belt covers almost all of the eastern third of 
ashington County. It enters from Pennsylvania as a broad belt, 
ing about 15 miles wide at the State line. It underlies the 
igerstown Valley, Antietam Creek running down the middle of the 
It for its entire extent. Hagerstown and Sharpsburg are located 
ar the middle of the belt; Blue Mountain, Edgemont, and Weverton 
} on or near its eastern edge, while Williamsport, Salisbury, and 
angansville are on or near the western border of the limestone. 
