MANSFIELD: ROXBURY CONGLOMERATE. 234 
the basin is partially separated from the sea by a constriction formed 
of ancient, highly metamorphosed, stratified rocks and a variety of 
intrusions, together with some granitic areas which are probably of 
great age (Shaler et al., p. 7). 
The north-south extension of the Narragansett Basin, including 
the Norfolk Basin, the axis of greatest length, is about fifty miles. 
The east-west diameter, from the western part of Cumberland, R. L, 
to Scituate, Mass., is about thirty miles. Although its outline has 
many irregularities, the basin has in general a rudely curved form, 
concave on the southeastern side (ibid., p. 8). 
Boundaries. The maps of Woodworth and Foerste in the mono- 
graph above mentioned show that the boundaries of the present sedi- 
Mentary area are generally true sedimentary contacts and are not 
marked by faults to the degree that seems probable in the case of the 
Boston and Norfolk Basins. Faults of the normal basin range type 
do occur at several places along the borders of the basin but their 
usual direction is north-south, with the downthrow on the east or 
west (Woodworth, d, p. 182), while the dominant direction of the 
probable faults in the Boston and Norfolk Basins is east-west, with 
the downthrow on the north or south. The irregularities of the 
borders of the Narragansett Basin are due largely to these faults. 
Sedimentary Series. The Carboniferous rocks of the Narragansett 
Basin have been divided into four groups by Woodworth in the north- 
ern part of the field and by Foerste in the southern area. The north- 
ern rocks have somewhat different facies from those of the southern 
area but the sediments of the two regions are believed to represent 
Synchronous deposition. The following account is taken from Wood- 
worth’s table (d, p. 134). 
In the northern area the lowest member, called the Pondville group, 
Consists of quartz conglomerates and arkose and has a thickness of 
about 100 feet. The Wamsutta group, consisting of conglomerates, 
sand$tones, arkose, shale, or slate, and beds of quartzite, accompanied 
by felsites, felsite breccias, and conglomerates, overlies the Pondville 
group, and has a thickness of about 1,000 feet. Some of the members 
Carry Calamites. The characteristic color of the series is red, but 
locally brown and green colors occur. Above the Wamsutta group 
come 10,000 feet of alternating beds of fine and medium conglomer- 
ates, pebbly sandstones, sandstones, and shales, with some coal beds. 
This group, known as the Rhode Island Coal Measures, has produced 
a considerable flora and fauna, the latter consisting largely of insects. 
The prevailing colors are black, blue, green, gray, and locally red. 
