F. Prime, Jr.—Lower Silurian Fossils. 267 
proportion of alumina which it contains. This also was to be 
expected if the subsidence continued, as signaling an approach 
to the era of slate-formation and open-sea deposition. These 
limestones are utilized on the Lehigh river in the manufacture 
of hydraulic cements and lately Portland cement has been made 
at the Copley Cement Works, which is said to be nearly or quite 
equal to the imported. Careful search and the demand for it 
will no doubt cause this variety of the limestone to be explored 
at various other points in the two counties, and will in time 
render us independent of the cement now sent from the Hudson 
River. The limestone is of a dull, earthy appearance, entirely 
free from any crystalline texture and of a dark gray color. 
Before closing our discussion of the limestone it is necessary 
to speak of the large and numerous deposits of brown hematite 
iron-ore which occur in it, and which form the main support of 
the extensive iron furnaces of the Lehigh and Schuylkill 
Valleys. : ; 
The brown hematite iron-ore occurs almost exclusively in 
two irregular lines of deposition; the one along the northern 
flank of the South Mountain Range, the other at or near the 
junction of the No. II limestone with the No. III slates. A 
few other localities, at which the ore is found, but these are 1n- 
significant in number compared to the two lines mentioned. 
with damourite; the same _ else 
brown hematite is found zn Joco originale. its ar 
however found which have evidently been pockets or cavities in 
the limestone into which the masses of limonite have been 
ing the Drift Period. 
let 
more especially potash, points to : 
from Archzean rocks containing orthoclase 
ecomposition of these three 
all the oxides above mentioned 
have been derived from iron pyrites, 
