66 PEARL SHELDON 
value. With these two sets belongs the second dip set found in 
other localities. 
JOINTS OF THE ENTIRE REGION 
Fig. 5 is a tabulation of all the strikes read throughout the Ithaca 
district, over three thousand in number. They are arranged in 
groups of five degrees each. It must be remembered that, with 
the exception of the six hundred also shown in Fig. 4, these joints 
were selected, so that the figure does not give a true record of the 
numerical occurrence of the various strikes but rather of the 
relative importance of the joints in each direction. 
Frc. 5.—Tabulation of the strikes of the joint planes of the Ithaca region 
STRIKE Jornts.—In the Ithaca region the strike set is the most 
important. Fig. 5 shows that for the entire area studied far the 
greater part of all the joints which may be considered as belonging 
to this set do not vary more than ten degrees in strike. As the 
figure shows, there is almost no tendency for the strike set to grade 
into the minor joints at each side. This set is even more sharply 
defined and easily recognizable in the field. 
The area studied was divided into squares of about a quarter of 
a mile on an edge. For Fig. 6 the readings of the strike joints in 
each small area were averaged together and the average is given 
beside a line drawn in the average direction. The center of the 
line is in about the center of the area considered and the width of 
the line is proportional to the number of readings included in the 
