22S Long iv ell— Structure of the Triassic 



oped to give definite inf ormation, but they at least suggest 

 that the lateral component of movement was negligible. 

 In most cases the throw is small, ranging from a few 

 inches to a few feet. The combined offset effected by the 

 ten faults between stations 9 and 11 is determined approx- 

 imately, by projecting dips. Before the construction of 

 the tunnel began, the surface of the ridge was surveyed 

 accurately, and the contact between the lava sheet and 

 the sandstone on the north slope was uncovered in order 

 to measure the inclination. Therefore the position of the 

 contact at the surface as indicated in fi.g. 2 is exact, and 

 the offset between this point and the base of the tunnel, 

 measured at right angles to the bedding, is 40 feet. Any 

 representation of the quantitative distribution of this 

 offset between the several faults involved can be sug- 

 gestive only, but it is probable that the greater part of 

 the throw is effected by one fault, the eighth in order 

 from the north. This fault is marked by abundant gouge 

 and a shatter zone of considerable width, features that 

 are absent or but faintly developed in connection with 

 the other dislocations. 



Possible Relationship to Larger Structural Features. 



Of course the section described above cannot be used 

 by itself as the basis for generalizations regarding 

 regional structure. Minor faults are numerous in the 

 Triassic of Connecticut, and many of them doubtless have 

 strictly local explanations. Development of joint sys- 

 tems may well have attended the warping shown in the 

 curvature of Saltonstall Eidge, and minor displacements 

 might be expected to occur either contemporaneously with 

 the formation of the joints or at a later date. However, 

 certain characteristics of the faults in the tunnel are 

 highly suggestive. All of the planes strike generally to 

 the northeast, all of them dip northwestward, and appar- 

 ently all represent normal faulting. It is natural, there- 

 fore, to attribute the entire group to a common cause. 

 A suggestion that this cause is local warping leads to 

 an examination of the Saltonstall "dish" as a unit. The 

 map shows a number of faults affecting the basin, but 

 all of them appear to strike northeastward. Fractures 

 developed as a consequence of the warping would be 



