54 PEARL SHELDON 
il 
INTRODUCTION 
In an attempt to find the age of the joint planes of the Ithaca 
region with reference to the low folds which occur here, observations 
were made on 3,046 joints. Nearly all of these readings included 
both strike and inclination, although in a few cases one or the other 
was necessarily omitted. Over six hundred readings were made in 
the Fall Creek gorge at localities 55 to 58 and part of 54 in Fig. 7. 
For this distance readings were made on every accessible joint 
which was strong enough to show for two or three feet and not so 
variable that the data would be of little value. Occasionally 
observations were made on more poorly developed joints which 
were locally characteristic. 
Although later work showed that this locality was hardly typical 
in some respects, this study showed how the joints of a single area 
vary with their strike and formed a basis for later work by showing 
which sets of joints are constant and strong and which too variable 
and weak to be of value in comparing different localities. During 
one summer and fall about two thousand readings, including this 
six hundred, were made in the Ithaca region. The following winter 
was given to experimental work and examination of the data already 
taken, and during the next summer another thousand readings were 
made in completing the section and investigating points connected 
with the theory, particularly the faulting. 
Only a part of even the master joints could be read in the field 
but those were chosen which local observation and work in neigh- 
boring areas showed to be most characteristic for each place and, 
because of their constancy, most valuable for comparison with 
other areas. The work was begun without a conviction in favor 
of any one of the theories for the formation of joints and most of 
the evidence of their age was unexpected, so that the choice of 
readings was influenced little by preconceived ideas. 
The data had a bearing on several points besides the age of the 
joints. The following are some of the results obtained: 
Nearly all the uniform and strong joints fall into two groups. 
