MANSFIELD: ROXBURY CONGLOMERATE. 287, 
by their tongue-like appearance on the polished surface and by the 
fact that in thin sections under the microscope they appear as irregular 
tongues of ferruginous glass, sometimes devitrified, with a well-devel- 
oped flow structure. It may perhaps be questioned whether these 
igneous intrusions are sufficiently basic to warrant their being classed 
with the melaphyrs, but since the latter are the only contemporaneous 
lavas yet recognized in this region, and since some of the impregnated 
rocks are near masses of melaphyr and their igneous constituents 
resemble some of the facies of that rock, it seems safe to conclude 
that the impregnations belong to the same series. 
On the other hand it is not equally certain that none of the lava 
in that section is effusive. As regards Crosby’s contention that the 
upper and lower parts of the melaphyr bands show differences in 
texture, the writer is not prepared to offer an opinion, since he has 
not carefully examined the localities noted; but with reference to the 
question of melaphyr pebbles in the conglomerate he can say that on 
the east side of Langley Street in Newton Center, three-quarters of 
a mile southeast of the railroad crossing, he found in a conglomerate 
ledge by the roadside a basic pebble that in thin section under the 
microscope appeared to be melaphyr. Thus the contention of Burr 
that none such occur seems a little sweeping. Probably the truth 
of the matter is that in this region both the intrusive and effusive 
types of melaphyr occur. 
——:— Summary of Relations to the Melaphyrs. At Nantasket, 
Hingham, and Hough’s Neck the melaphyr is believed to form flows 
interbedded with the conglomerate series. At Brighton the melaphyr 
appears to be intrusive. At Brookline and Newton there are many 
examples of igneous intrusion, where the igneous element is probably 
melaphyr, but the writer does not agree with Burr that all the melaphyr 
in this region is intrusive. Pebbles of melaphyr in the conglomerate 
indicate that surface flows also occurred. 
Metamorphism. he rocks of the Boston Basin are often said to 
be practically unmetamorphosed. Crosby, for example, states that 
in spite of the extent to which the rocks have been sheared, folded, 
and faulted there has been little or no regional metamorphism with 
the development of an indigenous micaceous element (n, p. 504). 
There are, however, abundant signs of incipient metamorphism that 
are worthy of notice. ; 
In almost every outcrop of the coarser members of the series planes \ 
of schistosity and cleavage are developed, which are often so perfect ' 
as to simulate stratification. Sometimes two or more directions of 
