MANSFIELD: ROXBURY CONGLOMERATE. 181 
as felsite areas are approached, so that no sharp lines of division can 
be drawn between conglomerate and felsite breccia or between the 
latter and true felsite. At Nantasket the ledges on the east side of 
Weir River near its mouth (Boston Bay VI, PQ 29) show conglomerate 
resting on granite. The conglomerate here might more properly be 
called a breccia but it shades upward with no well-marked line of 
separation into true conglomerate. The materials of the lower or 
breccia zone are largely granitic, similar to the underlying granite 
and felsite. The finer fragmentary material has been deposited in 
cracks in the granite, while larger masses are numerous in the debris 
B 
Fia. 5.— A. Contact of conglomerate and granite at Nantasket (slightly modi- 
fied from Crosby, m, p. 142). 
B. Conglomerate resting on fine (F) and coarse (C) granite (Boston Bay VI, 
2029) : : 
above the contact. This area has been described by Crosby, who 
states that the presence of felsite and melaphyr among the granitic 
debris indicates that the conglomerate at this point is not really basal 
