70) Ys PEARL SHELDON 
set has only a fair range of strike so that the two are entirely dis- 
tinct. ‘The line of the cliff lies between the two sets and the cliff 
face is in many parts composed of projecting and re-entrant angles 
formed by the joint faces of large area meeting in obtuse angles. 
The small number of readings made in that locality is due to the 
fact that these joints are mostly at inaccessible heights in the cliff. 
The directions are rather constant, however, so that the readings 
made are representative of all. 
The angle between the dip sets varies. Some of the averages in 
Fig. 7, which strike nearly north, come from observations too few 
in number to justify division into two sets. The resulting median 
value does not correctly represent either set if both are present. 
In other places, such as lower Fall Creek, there is a well-developed 
set whose average is nearly north, so that the angle between the 
two sets is only a few degrees. The upper locality at Willow Creek 
shows an unusually wide angle between the set. Those readings 
were made in the Tully limestone, and in the dip joints as in the 
strike joints the hardness of the rock seems to affect the direction. 
Unlike the strike set, the dip joints are better developed in the 
sandstones than in the shales. This appears where such layers 
alternate and also in the general distribution of the dip sets. In 
some of the softer shales along the lake they are rare and they are 
seldom so well developed there as the strike set. In the hard 
Portage rocks from the end of the lake southward the dip sets are 
far stronger than the strike. ‘The conspicuous joints seen in the 
gorges in the city of Ithaca are dip joints. 
The direction of the dip joints and the angle between the two 
sets seems to depend on the general force which caused the folding 
and the angle which the variable local resultant force made with 
it. ‘The two sets seem to be arranged on each side of a line which 
is a compromise between the two.” The range of the dip joints is 
from a line nearly perpendicular to the axes of the folds around to 
the east toward the perpendicular to the strike of the faults. The 
small angle between the sets near the city is probably related to 
the lack of strong folding there. In Fig. 5 the dip sets of the 
different areas overlap, obscuring their double nature. 
Hade of the dip joints.—The hade of the dip joints is in general 
