MANSFIELD: ROXBURY CONGLOMERATE. 203 
do occur, however, is shown by the anticline of slate in the railroad 
cut just south of the Neponset River at Milton. 
At Squantum the structure seems to be a prolongation of that just 
noted in the southwestern part of the belt. The dips are all southerly 
and more or less steep but the general structure seems to be anticlinal. 
The main characteristics of the structure at Squantum are thus out- 
lined by Crosby (ibid., p. 8): (1) the cleavage across the bedding of 
the slate; (2) the coarseness and irregularity of the conglomerate; 
(3) the repeated alternations of thin layers of sandstone and brownish 
Slate; (4) faults on a large and small scale; (5) closed and overturned 
folds. 
——:—The Neponset-Hough’s Neck Region. Between the Hyde 
Park Squantum anticline and the crystallines to the south there is a 
belt of slate that is relatively narrow in the west but broadens rapidly 
eastward. The general structure, according to Crosby (p, p. 35), 
is synclinal, but outcrops are few. In the western part of the area, 
near the granite, the slate is underlaid by arkose, which is somewhat 
kaolinized but is nevertheless quite granitic in appearance and the 
Whole shows a northerly dip varying from 40° to 70° (n, p. 479). 
Eastward along the granite boundary the arkose and overlying slate 
give way to conglomerate (ibid., p. 482) which, northwest of Presi- 
dent’s Hill, grades northward through various alternations into the 
main body of dark gray slate, with northerly dips of 85° to 90° (ibid., 
p. 484). The southerly dips of the conglomerate series of the Hyde 
Park-Squantum anticline on the north and the northerly dips of the 
Slates along the granitic border on the south form the basis for the idea 
of synelinal structure. The dips along the southern border appear 
to be somewhat steeper than those along the northern boundary so 
that in the western part of the area at least the syncline seems to be 
slightly overturned northward and has been so represented in the 
accompanying section (Plate 6). 
Eastward in the general direction of the strike of the conglomerate 
hear President’s Hill occurs the conglomerate at Rock Island, Hough’s 
Neck, with its associated slate and melaphyr. The interpretation 
of the structure of this area depends largely upon the view held regard- 
ing the nature of the melaphyr mass. The latter has been the sub- 
ject of some controversy, and has been considered both as a dike and 
as a flow. The melaphyr forms a ridge flanked on either side by con- 
glomerate passing into slate. On the south side this passage may 
actually be seen, but on the north side it does not appear, though its 
presence is inferred from the occurrence of low outcrops of slate on the 
