Ickel.] OREGON, PENNSYLVANIA. 279 
than 1 per cent of silica, alumina, and iron oxide. Its quality, quan- 
tity, and proximity to the railroad and to a series of shale beds' make 
It worth considering as a possible source of Portland-cement material. 
The same series of beds outcrop in the hills to the southwest and 
northeast and continue into Idaho, where they form important deposits. 
Large limekilns are now in operation at several points on this line of 
butcrop. 
Limestone deposits of considerable size occur in other parts of 
paker County, the most important at present being one which is 
Extensively worked for lime about 14 miles from Baker City. Other 
deposits occur in Grant County, and very thick and extensive beds of 
blue limestone are said to cover much of Union County. In Wallowa 
County deposits of marbles occur, which may be of service for cement. 
PORTLAND-CEMENT RESOURCES OF PENNSYLVANIA. 
PORTLAND-CEMENT MATERIALS. 
A number of limestones suitable for use as Portland-cement mate- 
ials occur in Pennsylvania, though only one of them has as yet been 
xtensively used for this purpose. For description these limestones 
nay be conveniently grouped as follows: 
(1) Trenton limestone (Ordovician). 
(2) Helderberg or Lewistown limestone (Silurian). 
(3) Carboniferous limestones. 
TRENTON LIMESTONE. 
DISTRIBUTION. 
The Trenton limestone, which furnishes the well-known u cement 
rock" of the Lehigh district, occurs in varying development in the 
ounties of Northampton, Lehigh, Berks, Lebanon, Dauphin, Cum- 
berland, Franklin, Lancaster, Center, and Blair, and to a much less 
xtent in several other counties of southeastern Pennsylvania. 
Throughout its range it is underlain by a highly magnesian (Kitta- 
tinny) limestone and overlain by a thick series of (Martinsburg and 
Hudson) shales and slates. Further details concerning its geologic 
occurrence in its most typical area will be found in the section on 
cement manufacture in the Lehigh district, on page 284. The distri- 
bution of the Trenton limestone in Pennsylvania is shown in a general 
way on PI. XIII. 
COMPOSITION. 
The Trenton limestone, wherever it occurs, is almost invariably low 
in magnesia, and is therefore almost always an excellent Portland- 
cement material. At times its value as a cement material is increased 
