238 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
structure and thickness indicate that the series was once continuous 
over the entire area. 
Relations to Igneous Rocks. In the Boston and Norfolk Basins 
extensive eruptions of acid lava preceded the deposition of the Carbon- 
iferous series and are abundantly represented in the conglomerates. 
In the Narragansett Basin similar lavas occur in the Wamsutta group, 
one of the lower members of the series. 
Basic lavas, intrusive or effusive, occupy an important place among 
the Carboniferous rocks of the Boston Basin. In the Norfolk Basin 
the only suggestion of their occurrence is the impregnation of the con- 
glomerate observed on the south slope of Bear Hill, and at two other 
localities. The amygdaloidal and scoriaceous dikes of diabase in 
the Wamsutta group at North Attleboro are the only representatives 
of these rocks known in the Narragansett Basin, and these may be 
of later date. 
Later dikes are numerous in the Boston Basin and are represented 
in the Norfolk Basin by the dike in the section north of Canton Junc- 
tion. Dikes occur in the Narragansett Basin but are not so numerous 
nor so important as those of the Boston Basin. 
Metamorphism. In all the regions under consideration metamor- 
phism has occurred to a greater or less extent. In the Boston Basin 
it is confined chiefly to shearing, together with some deformation of 
the pebbles of the conglomerate. The tendency of zonal arrange- 
ment indicates a close relation between phenomena of metamorphism 
and the axes of the folds. In the Norfolk and Narragansett Basins 
areas of intensely metamorphosed rocks occur where folding and 
deformation have been most intense but a large portion of each of 
these regions has been only slightly affected. 
Harvard Conglomerate. The Harvard Conglomerate is intensely 
brecciated and metamorphosed. It may be related to the Carbonif- 
erous rocks and structures worked out by Perry and Emerson in the 
vicinity of Worcester. 
HYPOTHESES OF ORIGIN. 
STATEMENT oF PROBLEM.— Thickness and Bulk of Sediments. 
It has been shown that in the Carboniferous basins great accumu- 
lations of sediment have. been formed. In the Narragansett Basin 
a preserved thickness of at least 12,000 feet is required by the present 
structure; in the Norfolk Basin probably 5,000 to 10,000 feet of beds 
are represented; in the Boston. Basin the maximum thickness, includ- 
ing the slates as Carboniferous, may be as much as 5,300 feet. 
— u. 
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