MANSFIELD: ROXBURY CONGLOMERATE. 207 
region is believed by Crosby to be a broken syncline (g, p. 13). The 
dips are steep northwesterly and almost isoclinal. The highly arkosic 
and felsitic character of the rock in the vicinity of granitic and felsitic 
areas indicates that the rocks in this region probably represent the 
basal portions of the series. The high dips and the highly meta- 
morphosed condition of the rocks show the intensity of the folding to 
which the latter have been subjected. 
——:——:— Hingham. The structure and stratigraphy of the 
Hingham rocks have been worked out in great detail by Crosby in 
one of his later papers on the Boston Basin. According to his inter- 
pretation an anticlinal axis, occupied by granite, extends in a nearly 
east-west direction north of the railroad and of Beal Street. At the 
western extremity of the axis melaphyr and sediments curve around the 
granite and dip away from it, forming the nose of an anticline. East- 
ward, in the vicinity of Hockley Lane, a transverse fault separates this 
area from one in which the order of succession is inverted and mela- 
phyr appears on the south side overlying the conglomerate. Probably 
the sediments in this belt are separated from the granite both north 
and south by important faults, bounded northeast by the great fault 
along the east side of Hingham Harbor. Northwest from the west 
end of the granitic axis a steep narrow broken monocline separates 
the granite from the trough holding the great mass of the slate. The 
faulted monocline contains a second band of melaphyr, which broadens 
northeast, forming the large quadrangular area east of Huit’s Cove. 
This area is bounded on all sides by downthrow faults. On the west 
the upper conglomerate and slate dip away from the melaphyr. On 
the north the downthrow of the sediments conceals the conglomerate 
and the slate lies against the melaphyr. On the south the narrow 
monocline separating the body of the melaphyr from the granite 
broadens until it reaches the fault at the northwest end of Squirrel 
Hill, where it changes, perhaps abruptly, to a broad and shallow syn- 
cline separated by a strike fault from the southerly monocline of con- 
glomerate and sandstone on the north. These features probably 
extend east under Broad Cove and Otis Hill. The monocline is 
clearly seen at Melville Garden and in the islands of the harbor. West- 
ward from the Garden the east-west strike and southerly dip change 
steadily but rapidly to a north-south strike and a westerly dip. 
Folds are the dominant structure of the Hingham area, but they are 
greatly modified by faults (Crosby, l, p. 200-202). 
The following table gives the Hingham section as determined by 
Crosby (ibid., p. 203) :— 
