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New England Railroad and the Neponset River, and east of 

 Blue Hill Avenue, extends across the course of this band of 

 slate, causing its lateral displacement toward the south ; and it 

 next appears on the south side of the river along the Shawmut 

 Branch of the Old Colony Railroad. Sandy beds in the vicinity 

 of the Mattapan Station on this railroad indicate that the slate 

 probably reaches as far west on this line as Blue Hill Avenue. 

 On the south side of the river it lies near, but not in contact 

 with, the petrosilex. This is a fine-grained bluish-gray and 

 greenish slate ; strike, N. 60°— 70° E. ; dip, nearly vertical. 

 It shows the usual passage into conglomerate, and can be traced 

 half the distance to the mouth of Pine Tree Brook, being re- 

 placed by conglomerate along the strike in that direction. 



On the north side of the river the contact between the con- 

 glomerate and petrosilex can be made out very satisfactorily. 

 The portion of the conglomerate lying immediately upon the 

 petrosilex is a true breccia holding large angular fragments of 

 the same petrosilex, and of amygdaloid. This gives way to 

 arenaceous beds showing a nearly vertical south-east dip. The 

 slate band is resumed again on this side of the river, appearing 

 north of River Street, and one-fourth mile west of Cedar 

 Street, as a homogeneous gray variety, with a high south-east 

 inclination, and a well-marked cleavage, which shows the usual 

 trend and dip. It is underlaid by conglomerate on the north ; 

 and the conglomerate on the south holds arenaceous beds, 

 which are characterized by the same dip as the slate. This slate 

 evidently continues but a short distance, when the band is again 

 thrown to the south side of the river, appearing along the rail- 

 road east of Pine Tree Brook. The slate is here thrown into 

 an unsymmetrical and faulted anticlinal fold, the axis of which 

 is cut out obliquely by the railroad. The strike is as above, 

 and the dip at the east end of the cut is southerly, 70°-80°. 

 Toward the west the beds gradually become horizontal, and 

 finally descend gently to the north. The rock is greenish-gray, 

 distinctly stratified, and well jointed. 



About the area of petrosilex and amydaloid on this side of 



