84 BULLETIN OF THE 



ingly systematic in direction, and all agree in having their uplift on the 

 southeast ; the complicated topography of the region is reduced to sim- 

 plicity ; and a limited power of prophecy is gained, as in the case of the 

 notch in the anterior ridge, just described. The key to the structure of 

 the region is discovered. When the walk southward along the back of 

 the anterior ridge is resumed, and the terminal bluff of South High 

 Rock is seen in its characteristic form, with Short Mountain rising be- 

 yond it, he must be indeed a sceptic who is not ready to predict that 

 yet another notch in the anterior with normal offset and overlap will be 

 found corresponding to this break in the main sheet. The notch (6) is 

 soon reached, but on looking eastward as usual for the heaved continua- 

 tion of the anterior, it is not to be found. The ground is low and open 

 to the foot of the main sheet of Short Mountain, and it is only to the 

 westward that there is any ridge (7) that may correspond to the ante- 

 rior. Just as our generalization was to be established we meet a de- 

 parture from it. The case is certainly of great educational value as well 

 as of geologic interest; and one must approach it with an excellent 

 geometric understanding of the several patterns of faults described on 

 the second excursion, if he would not be puzzled by its departure from 

 the topography of the faults thus far encountered. 



Turning westward instead of eastward, a ridge (7) is found that cor- 

 responds in every way with the anterior, and a brief consideration of its 

 position will show that it is an example of the case of Fig. 7, in which 

 the heave is on the northwest of the fault and the downthrow on the 

 southeast, the reverse of our usual style of dislocation. The offset is to 

 the west, or negative, instead of to the east ; and there is a lapse of 

 bluff front instead of an overlap. After perceiving this there is no 

 further difficulty. The main sheet of Short Mountain is seen to stand 

 farther west than the same sheet in the next block to the north, thus 

 confirming the conclusion derived from the anterior ; and when looked 

 at from the east, the backs of the two portions of the main sheet readily 

 disclose their relative altitudes : the southern is depressed compared to 

 the northern. The bearing of this reversed fault, determined by sight- 

 ing from the notch in the anterior through the pass in the main sheet, 

 is N. 65° E. It may be noted that if this course be turned a little to 

 the left, as if the fault curved to the north, it would lead in about three 

 miles to a peculiar fault breccia in the sandstones ; one of Percival's 

 " clay dikes," disclosed in a post-glacial stream channel, a mile south of 

 New Britain, at the eastern base of a great drumlin. The peculiarity 

 of this fault is that the deformation of the bedding on either side, shown 



