cc 
256 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
material. The great quantity of relatively large pebbles in the con- 
glomerate indicates vigorous erosion and rapid deposition. ‘The steep 
gradients required for the transportation of such materials, sometimes 
for great distances, as in the case of the muscovite granite at Attleboro, 
indicate that the material was derived from sources at sufficient eleva- 
tion to warrant the supposition of the existence of at least Alpine 
glaciers. ‘The occurrence of the Obolus pebbles in the conglomerate 
of the Narragansett Basin lends support to the view that some material 
may have been imported by glaciers from outside sources, but it has 
been shown (page 169) that these pebbles may have been derived 
from a neighbéring land mass not now extant. Perhaps the strongest 
argument for the agency of glaciers is found in the relative freshness 
of the granitic pebbles of the conglomerate and in the feldspathic 
character of the matrix. The feldspar fragments certainly often 
show signs of alteration, but when deposited they must have been 
practically fresh. The accumulation of so much coarse and fresh 
material means harsh erosion in certain areas and rapid deposition 
in adjoining regions. Such conditions are eminently characteristic 
of regions now subject to glaciation. The actual evidence of glacia- 
tion in the areas that furnished the debris might easily have been 
effaced by subsequent erosion; but the character of much of the 
remaining deposit is similar to that which might be laid by torrents 
overburdened by coarse glacial waste upon emergence from their 
mountain gorges. 
CoNCLUSIONs as To Orıcın.— The evidence adduced in the pre- 
ceding paragraphs is largely negative and unsatisfactory. The bed- 
ding and texture of the sediments, though attaining a fair degree of 
regularity, do not display these features in so high a degree of develop- 
ment as might be expected in true marine strata. The apparent 
gradation upward from coarse to fine texture in the Boston Basin, 
suggestive of marine transgression, is offset by the occurrence in the 
Narragansett Basin of a gradation in the opposite direction, sug- 
gestive of non-marine deposition. The fossils thus far found in 
the Narragansett and Norfolk Basins are indicative of non-marine 
rather than of marine origin. Similar evidence is borne by the 
irregularities of bedding and of texture. The lithological similarity 
of the Roxbury Conglomerate to the rocks of the Norfolk and 
Narragansett Basins makes it probable that all are of like origin 
and that the entire Carboniferous series of this region is non-marine- 
More than one process, however, was concerned in the formation 
