MANSFIELD: ROXBURY CONGLOMERATE. 159 
with sandstone. A specimen of grit from Brighton (Boston V, C 31) 
contains irregular streaks of finer material in the coarse. Another 
specimen from the same locality shows layers of fine sand with beau- 
tiful purplish laminae of silt shading into them. The layers are much 
contorted and interrupted. Grit occurs between the dissevered ends 
and fills in the irregularities. A detached fragment of the fine sand- 
stone also occurs in the grit. Still a third specimen from this locality 
shows lenticular development on a small scale, some of the lenses 
being not over an inch in length. Other specimens show some inter- 
bedding of coarser and finer sediments in the form of ill-defined zones. 
Cleavage is well developed in some of the specimens but usually forms 
an angle with the bedding in those cases where the latter can be deter- 
mined. The evidence from the specimens above noted goes to show 
that in some places the conditions of deposition were fairly constant 
but that in other places there was less uniformity. The contortions 
noted in one of the specimens from Brighton were probably produced 
during the deposition of the sediments, for the rock does not appear 
to be metamorphosed. The disturbance of the layers is such as 
might well have been produced on unconsolidated, subaqueous sedi- 
ments by the grinding action of stranded ice cakes. 
:— Relations to Melaphyr. The finer sediments show relations 
to the melaphyr similar to those above noted in the case of the con- 
glomerate. Specimens from the ledges in the vicinity of the convent in 
Brighton (Boston V, H 27) show contacts of the melaphyr with sand- 
stone that are very instructive. In one case the melaphyr contains a 
band of sandstone half an inch wide that has a dense ferruginous border 
one-eighth of an inch wide. Two small apparently detached, elongated 
areas of melaphyr within the sandstone near the border are also sur- 
rounded by the same kind of halo. In another case the melaphyr 
containing irregular amygdules of quartz and epidote cuts across 
the bedding of the sandstone. The layers are faulted and contorted 
near the contact. As the latter is approached the several layers bend 
and gradually become fused into a homogeneous, ferruginous mass in 
which the bedding can no longer be distinguished. Detached masses 
of sandstone are included in the melaphyr. The specimens show 
beyond question that the melaphyr in the. ledges from which they 
were taken is intrusive into the sediments. 
Summary of Roxbury Series. (1) Arkose occurs at several places 
in the Boston Basin. In some localities the feldspar is kaolinized but 
elsewhere, as at East Dedham, it is so fresh and the resemblance of 
the rock to granite is so marked that the arkose and granite are 
hardly distinguishable. 
