242 



Not only do all the circumstances of dip favor that view, but 

 the increasing fineness of this conglomerate toward the slate 

 points to the same conclusion. The slate almost as clearly 

 underlies the conglomerate on the north. According to Prof. 

 Shaler this was shown very distinctly when the bottom of the 

 Chestnut Hill Reservoir was exposed, and it may be seen now 

 along the eastern border of the reservoir. At the Newton 

 Centre ledge the superposition of the conglomerate is very 

 plain, but west of this the contact is not exposed again. One 

 of two things must be true : either the slate actually passes 

 beneath the conglomerate as it appears to do, or this appearance 

 is due to a complicated fault with the downthrow on the south. 

 Something may be said in favor of the latter view. 



At Newton Centre, as already stated, the slate appears to be 

 dislocated along the strike by a transverse fault, and the transi- 

 tion to the overlying conglomerate is very abrupt, with a very 

 evident, though slight, unconformability. At the Chestnut 

 Hill Reservoir, too, there are abrupt changes of dip ; thus the 

 most of the slate in and about the reservoir is inclined to the 

 north at low angles of fifteen to thirty-five degrees ; but on 

 the western side of the lower basin, just south of Evergreen 

 Cemetery, there is a small mass of gray slate with a northerly 

 dip of not less than seventy degrees ; while the conglomerate 

 of the northern band shows dips in the same direction, ranging 

 from thirty to seventy degrees. The passage here is sufficiently 

 gradual, being marked by several alternations of slate and con- 

 glomerates. This border zone is now well exposed in the em- 

 bankment on the east side of the reservoir, and PI. 5, fig. 2, 

 shows that we actually have at this point indubitable evidence of 

 at least local strike-faulting. The conglomerate in this section 

 is obscurely bedded, and the dip cannot be determined with 

 certainty ; but it is undoubtedly the same as that of the inter- 

 calated slates, which is variable and very high — seventy to 

 ninety degrees to the north. The joint or cleavage planes of 

 the slate, which have some resemblance to stratification, show a 

 northerly dip of about forty-five degrees. 



