218 



amyi^diiloidal, with many irregular veinlets and segregations 

 ot"ini[)ure epidote, etc., portions of the rock being of a distinctly 

 scoriaceous character. A coarse flow-structure is sometimes 

 indicated l)y the arrangement of the amygdules in i)arallel sheets 

 or layers, which have the normal dip of the section, S. ()0° or 

 more. As the map shows, the breadth of the belt varies, 

 perhaps, with the dip, from about IGO to more than 300 feet. 

 In the western group of ledges, a little north of the middle of 

 the belt, a thin layer of conglomerate, passing upward into 

 sandstone, the entire thickness being, possibly, less than ten 

 feet, interrupts the continuity of the melaphyr. This is the 

 normal reddish conglomerate, (-onsisting chiefly of granite and 

 felsite ; and it can not be classed as a tuff or a fragmental 

 mela[)hyr. The dip of the conglomerate is S. 60° ; and there 

 is no reason to doubt that it is essentially conformable with the 

 melaphyr above and below. But since neither contact is 

 clearly exposed, the facts are evidently insufficient to reveal 

 the true significance of the conglomerate. We can not deter- 

 mine conclusively whether it is a true interbedded conglomerate, 

 or simply an outlier of the very similar overlying conglomerate, 

 displaced by faulting. The latter view would readily explain the 

 unusual breadth of the melaj)hyr at this point ; and it may be 

 added that, independently of this conglomerate, there is no 

 special indication that the melaphyr is a composite flow. 



In the eastern group of ledges, in the angle between Beal 

 Street and Portuguese Lane, the contact of the melai)hyr and 

 overlying conglomerate is satisfactorily ex[)osed, and is decidedly 

 favorable to the view that the melaphyr is contemporaneous, 

 i. e., that the conglomerate has been deposited upon its surface. 

 The melaphyr is here very coarse and scoriaceous ; and the 

 numerous cracks and inequalities of its surface are tilled with 

 the finer part of the conglomerate, in such a way as to place 

 the relations of the two rocks beyond question. The conglom- 

 erate contains, however, comparatively little debris that can be 

 referred to this melaphyr; and this fact, together Avith the 



