Oe — ._- 
MANSFIELD: ROXBURY CONGLOMERATE. 247 
(5) The region was probably bounded on the east and southeast 
by more or less subdued mountains, or by a land area of sufficient 
height and extent to deprive passing winds of much of their moisture. 
HyporHeses or Oricin.— General Statement. The principal fea- 
tures that may be expected to appear in the various types of con- 
glomerate are shown in the tabular summary on pages 150-151. 
In the following paragraphs the characteristics of the sedimentary 
Series in each basin will be given in accordance with the items of 
the table, together with brief comparisons. 
Marine. Perhaps the clearest statement of the marine view of 
origin is given by Crosby. He claims that the stable marine condi- 
tions of Precarboniferous times gave way to an encroachment of the 
Sea upon the land, attended, however, by marked and oft-repeated 
oscillations of level, which spread sediments far and wide over the 
entire region (n, p. 461, 464). According to this view the conditions 
of deposition were like those under which the Cretaceous rocks of 
Texas were formed, as described by Hill. A comparison of the features 
of the Carboniferous sediments of eastern Massachusetts with the 
features of marine deposits as indicated in the table shows some 
Points of agreement, together with many differences. 
The matrices of the various conglomerates under consideration 
‚can scarcely be described as composed of clean sands. They ordi- 
harily contain much felsitic material and some feldspar and are com- 
Posed of grains not well sorted, but generally of variable size and with 
little appearance of arrangement. ‘The grains are usually angular 
or subangular and but seldom rounded. 
The pebbles, with the exceptions already stated (page 164), are of 
local materials. They are variable in shape and size and are on the 
whole subangular rather than well rounded. No markings other 
than pressure striations and indentations have been observed upon 
them. 
The colors of the Roxbury series are usually grayish, with reddish, 
purplish, or greenish tones, but the red colors are only locally intense. 
In the Norfolk and Narragansett Basins, however, extensive areas 
of deeply red colored sediments occur. 
Stratification is not well shown in the coarser conglomerates but is 
fairly well indicated where finer sediments appear. Cross-bedding 
IS seen in all three areas but it is not of frequent occurrence. In the 
oston and Norfolk Basins, so far as known, the coarsest sediments 
are at the base of the series and are overlaid by strata, which, with 
