168 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Felsite. 
Sources OF MATERIALS OF THE CONGLOMERATES. 
Many varieties of felsite are represented in the conglomerates, 
especially of the Boston and Norfolk Basins. The classification of 
these varieties and the study of their distribution in the conglom- 
erate, together with the determination, if possible, of the localities 
from which they were derived, form an interesting problem, but it 
involves detailed studies beyond the scope of this paper. In general 
it may be said that most of the felsitic pebbles resemble rock now 
exposed in the environs of the Boston Basin. This point, together 
with the fact that the conglomerate frequently becomes more felsitic 
in the vicinity of felsite areas and appears to grade into felsite breccias 
and then into felsite, indicate that much of the material of the con- 
glomerate was locally derived and not transported any great distance. 
There are some doubtful varieties of felsite that may or may not be 
represented by rocks now exposed in the vicinity of the Boston Basin. 
Such are certain pebbles collected by H. J. Wiswell from the Roxbury 
Conglomerate in the vicinity of the Bird Street station of the New 
York, New Haven, and Hartford Railroad. These pebbles present 
striking resemblances to certain facies of the Blue Hills porphyry 
but when compared in the laboratory with a number of specimens 
representing different facies of that rock they were not definitely 
identified. Fragments of the Blue Hills porphyry are not certainly 
known to occur in the Boston Basin but Crosby has vigorously asserted 
that this rock is abundantly represented in the pebbles of the Nor- 
folk Basin Conglomerates (n, p. 471). 
Quartzite. Several varieties of quartzite are represented in the 
conglomerates of all three of the basins under consideration and 
quartzite forms the principal rock in the pebbles of the Harvard Con- 
glomerate. From the abundance of quartzite pebbles in all the 
conglomerates it is certain that large areas of that rock must have been 
exposed at the time the pebbles were formed. Quartzite occurs in 
disconnected belts among the crystalline highlands to the north and 
west of the Boston Basin. ‘This points to the northern and western 
highlands as possible sources of that rock and to a southward and 
eastward transportation of the material. In the Narragansett Basin, 
on the other hand, the coarse upper conglomerates become coarser 
and more highly quartzitic toward the south, the very largest pebbles 
being observed in the Purgatory Conglomerate near Newport. These 
facts point to a southerly source for at least the upper conglomerate. 
The evidence from the fossiliferous quartzite pebbles favors the same 
view. These pebbles become more frequent in the conglomerate 
