170 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
north and south of the basins in question similar to pebbles included 
in the conglomerate, together with the intimate relations of conglom- 
erate, arkose, and granite at certain localities, as at East Dedham, 
again point to the local origin of the materials in the conglomerate and 
militate against the idea of transportation from a distance. 
In the Narragansett Basin the same granite appears in the pebbles 
of some of the lower members but in the Dighton Conglomerate at the 
top of the series no such pebbles occur. There is, however, at this 
horizon a considerable abundance of muscovite granite, not represented 
elsewhere in the series. Muscovite is also plentiful in the upper sand- 
stones and grits. The nearest localities known to the writer where 
rocks that could have furnished such materials are exposed are in the 
crystalline highlands northwest of the Boston Basin. If the rocks 
there exposed are considered as the source of the pebbles in the Digh- 
ton Conglomerate and of the muscovite in the sandstones it is necessary 
to assume the direction of transportation of the materials in the Narra- 
gansett Basin to have been from north to south rather than from south 
to north as indicated by the quartzite. On the supposition that the 
muscovitic material came from the north, its absence in the Boston 
and Norfolk Basins may be explained by the assumption that higher 
beds containing this material have been eroded away. If, on the 
other hand, it is supposed that the muscovite granite, like the Obolus 
quartzite, may have been derived from some land mass at the south, 
now no longer extant, it is difficult to account for the absence of the 
muscovite granite in the conglomerate at Purgatory. The latter is 
believed to be the stratigraphical equivalent of the Dighton Conglom- 
erate, though it has not been proved that such is the case (Woodworth, 
d, p. 184); if therefore both quartzite and muscovite granite came 
from the south it would seem that both should be represented in 
the conglomerate. Perhaps the Purgatory Conglomerate represents a 
lower horizon than the Dighton Conglomerate. If such were the case 
the muscovite granite may not have been exposed to erosion when the 
quartzite conglomerates were forming. In view of the stratigraphi- 
cal and structural relations made out by Woodworth and Foerste this 
supposition does not seem probable. It appears more likely that 
material was supplied to the conglomerate from both the north and the 
south. This supposition is favored by the decrease in the amount of 
muscovite granite southward and the increase of fossiliferous quart- 
zite in the same direction. The occurrence of the pegmatite pebble in 
the conglomerate of the Norfolk Basin (page 161) indicates that 
the muscovite rock series may not be entirely absent from the Norfolk 
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