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tion, to the diabase of Somerville and Medford ; and I have 

 ventured to refer it, along with that, to the Naugus Head 

 series. It crops at two points, about one-half mile apart, on 

 a north-south line ; and I have recently been informed, by Mr. 

 Cabot, that exactly the same rock occurs about a mile south- 

 west of this locality, on Lagrange Street. 



The Roxbury and Brookline conglomerate has the same wide 

 range in composition as that of other localities, pebbles of 

 quartzite, petrosilex, granite, and amygdaloid predominating, 

 as usual. At some points there is much pinite in both pebbles 

 and paste. The pinite pebbles are occasionally well rounded 

 and undistorted, but more commonly they are so compressed as 

 to partially envelop adjacent pebbles of harder material. The 

 physical characters of this mineral appear to be very constant. 

 Although, as a rule, the conglomerate of this area is decidedly 

 coarse, pebbles or boulders six to ten or twelve inches in diam- 

 eter being common in some parts, yet it is generally to be 

 observed that the texture becomes finer toward the northern and 

 southern borders of the belt. 



Along the middle of this conglomerate belt the beds lie nearly 

 horizontally ; but from this line the dip gradually increases on the 

 north to thirty or forty degrees, and on the south, as we have 

 seen, to nearly vertical. To the general view, at least, the 

 stratigraphy of this belt is exceedingly simple ; for it forms 

 a single broad, low, denuded, anticlinal fold. This arch is un- 

 symmetrical, the south side sloping down steeply to a nearly ver- 

 tical-walled synclinal, while the north side is characterized by 

 comparatively gentle dips at all points. The axis or crest of 

 the anticlinal is indicated by the tongue of petrosilex and amyg- 

 daloid projecting from Needham into Newton and Brookline, 

 and the band of level strata extending east on this line to Savin 

 Hill. It is in this part, where the lowest beds are exposed, 

 that we find the largest pebbles ; and, as we pass to higher 

 beds with steeper dips, toward the borders of the fold, there is, 

 to the general view, as just stated, a concomitant diminution in 

 the size of the pebbles. 



