MANSFIELD: ROXBURY CONGLOMERATE. 163 
grains the rock becomes a more normal sandstone. The fragments 
in both the grits and the finer sandstones are mainly angular and 
subangular and are not well sorted nor well arranged. The shales 
are sometimes arenaceous but generally they are argillaceous and 
well indurated. 
The colors of the finer sediments include purple, red, green, and 
gray. On the whole the purplish or reddish colors predominate and 
are more intense and more characteristic of the rock than in the Boston 
Basin. 
The bedding of the sediments of the Norfolk Basin is not usually 
well enough marked to be indicated in hand specimens, and will be 
detailed later when the field relations are treated. 
Reference was made in a previous paragraph to the evidences of 
igneous intrusion among the conglomerates. At the east end of 
Ponkapoag Pond there are several bold outcrops of red sandstones, 
shale, and grit. In one of the latter there are somewhat uncertain 
evidences of similar igneous impregnation. 
Summary of the Norfolk Basin Series. (1) The arkose at Pond- 
ville closely resembles granite. The contained feldspars are relatively 
fresh. 
(2) The matrix of the conglomerate resembles that of the Roxbury 
Conglomerate but is more feldspathic and contains a larger proportion 
of secondary minerals. The grains are variable in size, shape, and 
arrangement. 
(3) The pebbles are composed of practically the same substances in 
the same order as in the Roxbury Conglomerate. The specimens 
include one each of pegmatite and diorite. Along the south side of 
the Blue Hills the coarseness of the conglomerate exceeds that of the 
Boston Basin Conglomerate but elsewhere the two rocks are similar 
in that respect. The shape of the pebbles is usually subangular. 
Striations or markings are absent, except those due to deformation. 
Evidences of deformation are more marked in the Norfolk Basin than 
in the Boston Basin. 
(4) The finer sediments are somewhat feldspathic and composed 
of angular or subangular fragments. 
(5) The colors of the coarser sediments are prevailingly greenish 
gray and purplish, or reddish. In the finer sediments the red colors 
are more marked and form a more important feature of the rock than 
they do in the Boston Basin. 
(6) The specimens examined show a less degree of assortment and 
arrangement than the specimens from the Boston Basin. 
