166 ANNALS NEW YORK ACADEMY OF SCIENCES 



Chas. M. Wheatley, in his studies at the Phoenixville tunnel in 1861, 

 observed this phenomenon, which has been found to be very common 

 throughout the extent of the Lockatong rocks. In the tunnel he found 

 "olive green shale, with red veins," and above it, ^'red shale." Ked 

 stringers in olive green rocks, or angular fragments of the green material 

 in a reddish matrix, are often in evidence. Eed fragments in a green 

 matrix, or green filling in red rocks, has not been observed by the writer, 

 although such a phenomenon is recorded by Dr. Kiimmel.^^ 



Tectonics 



There are, in the Lockatong rocks, three principal directions of frac- 

 ture. The first of these marks the lines of original bedding in the strata, 

 and along this series, except in a few cases, little movement has taken 

 place. The major joint series, which is strongly developed, causes a sepa- 

 ration along parallel plane surfaces nearly at right angles to the bedding. 

 There is also a parting at right angles to the other directions named. 

 The blocks resulting from fracture in these three directions are rectangu- 

 lar in shape, seizing most admirably the purposes of building construc- 

 tion. Such fracture as is here described is perhaps best shown in the 

 "flagstone" layers of the formation. 



The major joint series strikes usually forty degrees, more or less, east 

 of north. These are usually vertical, clean-cut joints. At an angle of 

 about twenty degrees to the major joint series there is a minor series of 

 joints, striking, in the Princeton area, from due north to north forty de- 

 grees east. This series has a dip of seventy-five degrees toward the east 

 in the case cited. It can be seen on a large scale in Shanley's quarry at 

 Byram. Two joint series at a relatively small angle to each other may be 

 explained by the theory of "rotational strain," as put fonvard by C. K. 

 Leith.^*^ At times an incipient slaty cleavage occurs, having a diagonal 

 direction, and causing the argillites and shales to develop deeply fluted 

 surfaces of parting along joint planes. 



Nothing has been seen either in the rock sections or in chemical work 

 on solid chips, which would indicate any important arrangement of the 

 exceedingly small grains, save in the direction of the bedding. Therefore 

 it appears that the direction of the major joint series must be independ- 

 ent of the smaller structures of the rock itself, i. e., that the cause of its 

 direction must be looked for without. 



Along the major joint series there has been some movement. This has 



19 Ann. Kept. State Geol. N. J., 1806, p. 44. 



20 "Rock Cleavage." V. S. Geological Survey, Bull. 230, p. 112. 100.^). 



