176 PEARL SHELDON 
the dip joints seems to be mainly in the same direction as the pitch. 
At any rate, their hade is not such as would be produced by sub- 
sequent uplift of joints formed with uniform, nearly vertical 
inclination. 
As in the case of the strike joints, the upper limit is set by the 
faulting. They cannot be older than upper Devonian, the age 
of the rocks in which they occur. One set of dip joints is nearly 
at right angles to the axes of the folds and the other set lies near 
the local resultant force acting during the folding as indicated by the 
strike of the faults. The angle between the two dip sets varies 
with the intensity and pitch of the folds. They are not so well 
differentiated near the weak Watkins anticline as near the strong 
and pitching Shurger Point fold and the strong Alpine anticline 
south of the Enfield syncline. The comparative strength of the 
two sets varies also. The experimental work showed that a varia- 
tion in the forces at right angles to the active pressure had a large 
effect upon the cracks. The pitching of the folds and the large 
angle shown by the faults between the local resultant force and the 
general force at right angles to the axes of the folds indicate that the 
forces at right angles to the pressure varied considerably from place 
to place during the folding. Under such conditions the two dip 
sets would be expected to differ in strength and to vary with the 
folds if they were formed at that time. 
The experiments showed that subjecting paraffin and resin to 
pressure gave fine cracks at right angles to the pressure and nearly 
parallel to the pressure. The latter were developed from a double 
set bisected by the line of pressure and might themselves form a 
double set if they could be measured carefully. During the 
Appalachian Revolution such a horizontal pressure was applied to 
the strata and should have formed cracks having directions like 
the observed joint planes. It has not been shown that there was 
enough disturbance of this region between the time of deposit of 
the rocks and the formation of the folds to have produced joints. 
If that were the case two independent groups of strike and dip 
joints should be found, for experimentally both strike and dip 
cracks were formed by a single application of pressure. There 
are two sets of dip joints found but they seem to be too close-y 
