78 PEARL SHELDON 
joints are only approximate because the exposures are usually poor. 
The rock walls quickly fall where these large diagonal planes for 
slipping are present. These highly inclined joints are not uniform 
in direction and a single joint is usually a curved instead of a plane 
face. They seem to be associated with the stronger folding. 
Among the smaller joints of interest are certain offshoots from 
the dip joints. In an area where nearly all the dip joints belong to 
Photograph by G. D. Harris 
Fic. 8.—Jointing on the east shore of Cayuga Lake. The joints are not at right 
angles to the stratification but are inclined in the same direction as the beds. 
one set but where there is an occasional example of the other set, 
or where the dip sets vary from their usual direction, the less usual 
joints sometimes have small cracks running off diagonally for a 
few inches in the more common direction of the dip joints. 
Of the joints with no apparent uniformity perhaps the most 
interesting are the smallest. Some of the rocks, especially the 
Hamilton shales, are broken by a mass of tiny, smooth, curved 
faces of only a few inches in area. These are the faces along which 
the shale parts when it crumbles. They have no apparent system. 
