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pages concerning the structure of, and volume of strata involved 

 in, the other broad areas of conglomerate characterized by a 

 monoclinal dip. In this Brighton district, and also in the 

 Nantasket area, the faulted structure may have, perhaps, an 

 extreme development, as regards the number of fractures, or 

 amount of dislocation, or both ; and yet I believe that the same 

 type of structure, although far less evident, characterizes a 

 large part of the Boston basin. 



The scale of the map is too small for the accurate delineation 

 of the rocks of this complicated area ; but the general outlines 

 given suffice to show the plan of the structure. The portion 

 of this conglomerate belt mapped as occurring in Brookline is 

 hypothetical, with the exception of an outcrop on the western 

 end of Corey's Hill, arid several ledges on Washington Street. 

 There are magnificent exposures of the conglomerate on this 

 line south of Washington and Union Streets in Brighton ; and 

 the dip, wherever observable, is about thirty degrees to the north. 

 On Breck Street, in the angle between Washington and Allston 

 Streets, the conglomerate, small-pebbled and arenaceous, is 

 overlaid by perhaps two hundred feet, traverse measure, of a 

 soft, homogeneous, pure gray or slightly greenish, slate. It is 

 thin-bedded, and dips N. 35°. The actual contact with the 

 conglomerate is not seen on either side, though ledges of this 

 rock approach very near on both the north and south ; but the 

 slate is probably cut off by a fault in the direction of the dip, 

 and does not underlie the conglomerate to the northward. The 

 rock exposed between Washington and Warren Streets is 

 mainly conglomerate ; but on Allston Street, between Summit 

 Hill Avenue and Warren Street, and north of the line of strike 

 of the slate on Breck Street, there is brownish and grayish 

 slate. The bedding is distinct, but shows immense disturb- 

 ance, standing nearly vertical, and striking toward all points of 

 the compass. This slate has a well-marked, but irregular 

 cleavage dipping north-north-east about forty-five degrees. 

 Nearly due east of this, in the large gravel quarry on Win- 

 chester Street, the same slate, but perhaps a little less dis- 



