252 BULLETIN: MUSEUM OF. COMPARATIVE ZOÖLOGY. 
No other aqueous agency than the sea appears to have been con- 
sidered but it will be observed by reference to the table, pages 150- 
151, that the features indicated by Crosby are not confined to ma- 
rine conglomerates. The main arguments in favor of marine origin 
seem to be: 
(1) the apparent gradation upy ‘ard from coarse to fine texture in 
the Boston Basin and in the northeast part of the Norfolk Basin; 
(2) the prevalence of banding as the type of bedding, indicating 
a tendency to regularity rather than to irregularity of stratification; 
(3) the distribution of lenses, so far as observed, in the same hori- 
zon or in parallel horizons, showing a similar tendency. 
The argument of gradation upwards in texture from coarse to fine 
does not hold for the Narragansett Basin and the southwest part of 
the Norfolk Basin, for in the former case the coarsest conglomerates 
lie at the top of the series and in the latter case arkoses and finer sedi- 
ments lie at the base, while coarse conglomerates of uncertain strati- 
graphic position occur apparently higher in the series. Moreover; 
it is not certain that the upper part of the Carboniferous series is seen 
in the Boston Basin. If the crystallines of the northwest highlands 
are the source of the muscovitic material of the Narragansett Basin, 
the absence of such material from the Boston Basin must mean that 
the muscovitic rocks to the northwest were not exposed to erosion 
at the time the present sediments of the Boston Basin were forming, 
and that the latter rocks are not the equivalents of the upper members 
of the Narragansett Basin series, but are stratigraphically below them. 
In that case the upper members of the Roxbury series have probably 
been removed by erosion and they may ‘have been coarse in texture 
like the upper strata of the Narragansett Basin. The arrangement 
observed in the Narragansett Basin is the normal order in fresh-water 
deposits but unlike the usual succession of marine strata. 
If the deposits of the entire region were the result of the encroach- 
ment of the sea upon the land it is difficult to account for the presence 
of such large pebbles of muscovite granite and quartzite, as appeal 
in the Dighton Conglomerate at Attleboro, so far from their apparent 
sources. Pebbles eight inches or a foot or more in diameter coul 
not have been dragged twenty or thirty miles by marine waves and 
currents. Some other agents, such as rivers or glaciers, must have 
transported the material from its sources and delivered it to the sea, 
if it were the latter that really resorted the debris. But the litho- 
logical study of the rocks of the several basins has shown that the 
component materials are less well rounded and assorted, and less 
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