THE SLATE INDUSTRY AT SLATINGTON, PA., AND MARTINS- 
BURG, W. VA." 
By T. Nelson Dale. 
SLATINGTON, PA. 
The basis of the slate industry here is a belt of Lower Silurian 
(Hudson) slates, shales, and grits which stretches along the southern 
side of the Blue or Kittatinny Mountain from east-northeast to west- 
southwest. This formation is about half a mile thick, overlying the 
great magnesian limestone formation on the south and underlying the 
Upper Silurian conglomerate and sandstone on the north. The struc- 
ture of this formation is a succession of minor folds generalty over- 
turned to the north, and in places crossed by a southward-dipping 
slaty cleavage. 
Although the formation covers many square miles of Lehigh County, 
west of the Lehigh River, and prospects have been made at man}^ 
points, yet the Slatington industry is confined to an area of 3 to 4 
square miles along Trout Creek and its branches. Within that area 
about 100 openings have been made, of which only about 45 are now 
being worked. These range from 50 to 300 feet in depth. 
The slate is black and has a very fine cleavage. It is calcareous, as 
shown by its effervescing in cold dilute hydrochloric acid, and contains 
carbonate of iron, as shown by its discoloration after continued expo- 
sure. Under the microscope it is found to consist of a matrix of mus- 
covite (potash mica), with much carbonate, carbonaceous matter, and 
pyrite, some angular quartz and feldspar grains, chlorite scales, and 
the usual slate needles (rutile, Ti0 2 ). It is geologically between a 
phyllite and a clay slate. The roofing-slate industry here seems to 
owe its success largely to the fine cleavage, which enables the pro- 
ducers to undersell slates of more durable character, but of poorer 
fissility. Some beds unsuitable for roofing are made into school 
slates. A large establishment for the manufacture of school slates 
has just been erected. 
The slate beds vary in thickness and alternate with grit beds from 
a fraction of an inch to several feet in thickness. The gril consists 
mainly of quartz grains, carbonate, carbonaceous matter, and pyrite. 
It represents coarser marine sediments, brought in possibly by shift- 
'i Detailed reports on these areas are in preparation. 
361 
