= 
MANSFIELD: ROXBURY CONGLOMERATE. 249 
the base, to fine above, in accordance with the idea of marine trans- 
gression; but in the Narragansett Basin the coarsest sediments over- 
lie rocks of finer texture, in conformity with the normal cycle of fresh- 
water deposition. The few instances of limestone deposits show no 
sign of organisms, either fresh water or marine. 
Estuarine. Perhaps the most abundant and distinctive component 
of estuarine deposits is fine mud. Argillaceous materials are repre- 
sented to some extent in the matrices of the various conglomerates; 
they are not particularly abundant. In certain places, however, 
the matrix of the conglomerate appears to be felsitic, and it may be 
that before consolidation this material was a felsitie mud. Fine 
gravel and sand are certainly represented in the conglomerates of 
the three basins and the grains of the matrices are usually angular, 
subangular, and ill sorted, but they are not ordinarily cross-stratified. 
The pebbles of the various conglomerates might agree well enough 
with the expected characteristics of estuarine conglomerates. They 
are of local materials, with the exceptions noted, of variable size, and 
hot well rounded nor sorted. 
So far as color is concerned, the conglomerates in question would 
Meet the expectation of estuarine conglomerates, for red colors occur 
m each basin. 
Frequent and irregular bedding of coarse sands and finer materials 
may be said to occur in some measure among the finer sediments 
of the several series, but it cannot be said to be so marked a charac- 
teristic as is implied in the table. Cross-stratification, which should 
Occur frequently in estuarine deposits, is only an occasional feature 
of the rocks under consideration. Ripple-marked surfaces, with sun- 
cracks and other markings, which should appear frequently in 
estuarine sediments, are of relatively uncommon occurrence in the 
Carboniferous rocks of the several basins. 
Fluviatile. With the exception of cross-stratification, the features 
of the matrices of the several conglomerates agree well with the expected 
tatures of fluviatile conglomerate; for they consist of sands mingled 
With finer and coarser material, in angular to subangular grains, not 
well sorted. 
The pebbles, too, conform with the description of fluviatile deposits. 
t any outcrop of conglomerate the pebbles usually present a wide 
Variation in size, sometimes, as at Squantum, Hingham, and Purga- 
tory, exceeding one or two feet in diameter. In general the pebbles 
of the conglomerates of the several basins are subangular but they 
Present all shapes from angular to rounded. Moreover, fragments 
