MANSFIELD: ROXBURY CONGLOMERATE. 251 
Spond well enough with those indicated as characteristic of glacial 
deposits; for in many places the rocks are dark gray with greenish 
tints and sometimes with bluish tints. The very noticeable red colors 
of other portions of the series do not, however, agree with the ordinary 
colors of glacial deposits. 
The conglomerates of all the basins have been shown to exhibit 
some degree of bedding, but the latter is often poorly defined. Occa- 
sional pockets and lenses of coarser and finer material, with cross- 
bedding, occur in the less well stratified masses. In this respect 
they seem to resemble both fluviatile and glacial deposits. There 
is no case where large boulders have been observed in the midst of 
fine and evenly bedded deposits, but there are localities where pebbles 
a foot or more in diameter are scattered through finer conglomerate 
or grit that is poorly bedded. 
The conglomerates have nowhere been observed to lie upon glaci- 
ated surfaces. In all cases where the basal contacts have been ob- 
Served, the underlying rock has shown evidence of subaérial decay. 
GENERAL Discussion. — General Statement. In the foregoing 
Comparison of the Carboniferous conglomerates of this region with 
the characteristics of the various types as outlined in the table it has 
been shown that the former have some resemblance to each of the 
given types, and that there is no case where the correspondence is 
complete. Probably, then, the conglomerates have been formed by 
the combined action of two or more of the given processes. It now 
remains to consider the above comparisons in connection with other 
general data and to discuss the relative merits of the several hypo- 
theses of origin. 
Marine. The writer has seen no clear statement of the argument 
for the marine origin of the conglomerate. Such origin seems to 
have been assumed from the general water-worn condition of the 
Pebbles in the conglomerate and from the present proximity of the 
Sea. In an argument against the suggestion of glacial origin, Crosby 
Cites the following facts in favor of the marine idea: (b, p. 187): — 
(1) the lithologie passage from conglomerate to slate. : 
(2) the undoubted conformability of the slate and the conglom- 
erate. 
(3) the evident stratification of the conglomerate. 
(4) the absence of striated pebbles. 
(5) the local origin of the materials. 
(6) the evidence of sorting by water. 
