| x 76 
probable that almost the entire basin of Strait's Pond is under- 
lain by this conglomerate. It is this view of the geological 
the fault-lines on the map. Of course, if the conglomerate is 
| carried down to any considerable depth by the rather high dip 
| which it shows near Jerusalem Road, it is very probably covered 
| in the central part of the basin by the overlying melaphyr. 
The Western Area. 
This area comprises all that part of Nantasket proper west of 
the railroad. It is bounded on the south and west by Weir 
| River Bay, and on the north by Nantasket Harbor. We have 
| already met the fundamental granite along the southern margins 
of the central and coastal areas; but it is in the western area 
| that we first encounter what appear to be the oldest beds of 
| conglomerate and melaphyr in the Nantasket district. The 
| geological structure is quite as varied and complex as in the 
central area, and as before, the descriptions may most conven- 
iently follow the topographic order. 
|| Granite Plateau.— This is the name given to the largest 
| mass of granite in the Nantasket peninsula. It forms the large 
li southwestern angle of the western area, and is a compact eroup 
| © © 
of ledges having, for the most part, an elevation of from twenty 
to forty feet. The granite is of the normal type, and, exhibiting 
but slight variations, requires no special description ; but the 
outliers of conglomerate scattered over the plateau are a feature 
| of particular interest. The more important of these are indicated 
on the map; and the best and clearest exposures are, naturally, 
to be found along the shore. The conglomerate is most abun- 
dant around the northeast. corner of the plateau, where it shows 
east and southeast dips of 5°—10°, and a maximum thickness of 
|| perhaps 15 feet. Elsewhere it is hardly thick enough to conceal 
the granite; and everywhere it is largely composed of angular 
ranite. This is 
and unassorted débris of precisely the same g 
| stucture that is intended to be expressed in the arrangement of 
