у 
—h 
121 
meets the great dike of the second system (46). It is some- 
what branching as well as porphyritie, and crosses the channel 
without sensible displacement, although it is somewhat jogged 
in the plateau. The E.-W. dike (39) in the granite south of 
the west marsh is imperfectly exposed; and its chief point of 
interest is that it cuts the great melaphyr dike (2). 
The dikes beyond the east marsh (40 and 41) have rather 
noncommittal trends, not belonging distinctly to either system. 
These are, possibly, extensions of the Great Hill dikes ; but it is 
impossible to prove it. They converge eastward and upward. 
The dike in the granite southeast of Round Hill (42), on the 
other hand, is, so far as can be seen, a very typical example 
of the first system. 
The most northerly dike of the second system in this belt is the 
smallest one, the solitary dike on Crescent Hill (48). It can 
be traced continuously across the conglomerate and melaphyr 
from the western to the eastern face of the hill. If it were con- 
tinued across the railroad in the same direct line it would strike 
Great Hill about 40 feet from the northern end ; but no trace of 
it could be found in the bare ledges of conglomerate and sand- 
stone. Advancing south across Great Hill, we come first to 
dikes 44 and 45, which, as already stated, appear to be cut by 
37 of the first system.. These two dikes are somewhat con- 
verging eastward, and 44 ends very abruptly in the conglom- 
erate before reaching the face of the hill. The principal dike 
of this entire belt is 46, which begins on the western shore of 
Granite Plateau with a breadth of about 12 feet. It is jogged 
to the north 8 or 10 feet in ascending the slope, and cannot be 
clearly traced more than half-way across the plateau, passing 
under the grass; but there is a natural path for it under the 
narrow meadow along the north side of the high, precipitous 
ledge of granite and conglomerate to the western marsh. 
Here it is directly in line with what is clearly the same dike in 
Great Hill. On the precipitous western face of Great Hill, 
just north of the junction of the conglomerate and granite, it 
