PENNSYLVANIA, 
83 
from 35° to 75°. There is sometimes a difference in the angle of the cleavage dip 
in adjacent beds. The curvature of the cleavage at the "Old William Hughes" 
quarry amounts to a change of 20° in 25 feet of slope. There is apt to he a little 
curvature of the cleavage on either side of the ribbon. There is a conspicuous sys- 
tem of dip joints striking about north-south, some of which are shown in Pis. X \ 1 1 
Fig. 8.— Sketch of syncline at William Hughes's quarry, near Slatington, Pa. Looking west. 
Length, 80 feet. Upper bed over 10 feet thick; lower bed 15 feet thick, but with marked curvature 
of cleavage. 
and XVIII. There are- also strike joints which sometimes undulate like bedding 
planes, as at the Eureka quarry (PL XVIII). 
The names of the Slatington beds are, from south to north, the Williamstown, 
Blue Mountain, Trout Creek, Washington, Little Franklin, Big Franklin, Mammoth, 
New Bangor, Snowdon, and Eureka. It is uncertain whether some of these are not 
Fig. 9.— Sketch of folds at Eureka quarry, near Slatington, Pa. Looking east. Length, 350 feet; 
depth, 225 feet. The upper part of the syncline is shown in PI. XVIII. 
duplications, for the structure of the belt, as shown in the section on PI. XVI, indi- 
cates that they may be, and their relations have never been worked out mathematic- 
ally. Examples of these beds ("veins") are the Washington, which at the Hazel 
Dell quarry averages 27 feet in thickness or 40 feet measured along the cleavage, and 
the Franklin, at the "Old Franklin" quarry, which consists of an upper bed of 28 
