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amygdaloid axis, but also toward the east. This may be the 

 result of increasing distance from the ancient shore line, or of 

 a declination of the axis in that direction, so that the beds 

 exposed on the crest of the fold in Dorchester overlie those on 

 the same topographic level farther west ; the latter view appears 

 most probable. 



The low dips, and in many cases entire absence of inclination, 

 characterizing a large part of the Roxbury and Brookline con- 

 glomerate, afford the principal basis for the prevalent idea that 

 this rock is newer than and overlies the highly inclined slates 

 on either side ; but I fail to see that this view is warranted by 

 the facts indicated. Along the middle of the belt the evi- 

 dence is plain that the conglomerate simply forms a broad, 

 low, flat-topped arch ; but towards the borders all the circum- 

 stances of dip and texture lend unequivocal support to an 

 opinion the contrary of that commonly held. The fact is 

 that, as I have frequently stated, as regards both dip and 

 strike, the conglomerate and slate seem to be everywhere per- 

 fectly conformable ; and the former underlies, always, save where 

 the strata are faulted or inverted, dipping toward the nearest band 

 of slate ; while the slate just as invariably dips away from the 

 nearest conglomerate. I am speaking now with special refer- 

 ence to this large area of conglomerate and the slates which 

 border it ; and yet I consider that, with some unimportant 

 exceptions, which are more apparent than real, the foregoing 

 statement holds true for the whole Boston basin. 



The Upper Falls, Chestnut Hill, and Boston Slate Belt. 

 — Boston proper, South Boston, and the northern half of Rox- 

 bury, are unquestionably underlaid mainly, if not wholly, by 

 slate ; but, since these districts constitute a region of almost 

 unbroken drift, and the first rock met on the south is 

 conglomerate, the determination of the boundary between the 

 Roxbury conglomerate and the slate is largely a matter of con- 

 jecture. The magnificent ledge of conglomerate west of the 

 Roxbury station, on Tremont Street, formerly extended as far 

 north as Conant and Station Streets ; and conglomerate ledges 



