. Bulletin - New York State Museum. Science. 486 NEW YORK STATE MUSEUM they are found to run in all possible directions [fig. 2]. In individual exposures the majority of the joints are seen to be curving instead of straight. This shows that some latitude in direction must be allowed each joint set, but is not decisive as to the amount of allow- ance necessar}^ Few exposures show more than two good sets of parallel joints, though some show three and even four. Certain compass directions are frequent in certain portions of the quad- rangle, and utterly fail elsewhere, indicating a shifting of di
. Bulletin - New York State Museum. Science. 486 NEW YORK STATE MUSEUM they are found to run in all possible directions [fig. 2]. In individual exposures the majority of the joints are seen to be curving instead of straight. This shows that some latitude in direction must be allowed each joint set, but is not decisive as to the amount of allow- ance necessar}^ Few exposures show more than two good sets of parallel joints, though some show three and even four. Certain compass directions are frequent in certain portions of the quad- rangle, and utterly fail elsewhere, indicating a shifting of direction, rather than a different joint set, it is thought. From the best ex- posures it can be learned that in general there are two sets of joint couples, each couple consisting of two sets of parallel joints which. Fig. 2 Diagram of the readings on joints within the Long Lake quadrangle. The inner figures represent the compass degrees east and west of true north; the outer row the num- ber of joint readings observed for each s° direction. Four numerical groups are also indicated. approximate a right angle with one another, and that one couple tends to occupy the meridional and equatorial directions, the othet running northeast and northwest. An attempt may be made to classify the entire number of readings on this basis, assuming that each set has a variation in direction of 20° owing to swerve. Thus the n. 80° e. to n. 80° w. joints are grouped together, forming a couple with then. 10° e. to n. 10® w. joints; in like manner the n. 40° e. to n. 60° e. and n. 30° w. to n. 50° w. joints are grouped. The numerical results of this grouping are indicated in the diagram, and a greater number of the readings are included, on this basis of subdivision, than on any other possible basis using the same amplitude of swerve. It is quite certain that some of ^the joints have a swerve of this amount, but it is not impossible that they may have even Please note that these ima
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