OBSERVATIONS AND EXPERIMENTS ON JOINT PLANES. 77 
larger and less uniform than in the strike joints. In some places 
in the Portage rocks where the dip joints are strong and occur at 
regular intervals, forming joint-faced buttresses along the gorge 
walls, the angle is quite uniform and nearly vertical. These evenly 
spaced joints occur in Fall Creek, Glenwood Creek, and in the 
Portage beds in the Taughannock gorge. 
A detailed study of the pitch of the folds is necessary before the 
meaning of the hade of the dip joints will be clear. In general the 
hade of the joints and pitch of the rocks seem to be in the same 
direction, though some local measurements were opposite. The 
joints as a rule are not perpendicular to the bedding planes. 
Some of the larger angles of hade are associated with faulting. 
This is true along University Avenue in Ithaca (localities 67 and 
68). It is more conspicuous at Taughannock Falls where joints 
with a vertical exposure of two hundred feet or more are nearly 
vertical at the top of the gorge wall and bend to an unusually large 
angle with the vertical near the base where several nearly hori- 
zontal faults are present. This is probably due to drag along the 
faults. 
Minor Jornts.—Besides these fairly constant sets there are 
minor joints striking in every direction, but they are as a rule 
easily distinguished from the major sets by the fact that few of 
them are to be compared with the major joints in strength and 
especially by their irregularity and usually large hade. Near the 
Shurger Point anticline is a set of minor joints which are comparable 
with the major sets in strength. These joints vary widely in 
direction, but ordinarily make a fair angle with the strike and dip 
sets and always have a large inclination, from 30° to 60°. The 
strike is both N.E. and N.W. and the hade may be to either side 
in the joints of either direction. High-angled joints similar to 
these were seen in other parts of the area studied but usually not 
so well developed. In Salmon Creek highly inclined joints of about 
this strength are frequent but their direction is nearly the same as 
that of the regular strike set. In fact, some of them seem to be 
continuous with strike joints which are nearly vertical for part of 
their height, then suddenly bend to a high angle and probably 
change their direction somewhat also. Measurements on these 
