188 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
Hoppin Hill. The rock is massive and fine grained, varying from 
green to brown in color. The massive structure and the angularity of 
the particles of quartz and feldspar seen under the microscope make 
it likely that it is to be regarded as an ash deposit accompanying the 
felsite flows of the northwest corner of the basin (Woodworth, d, p. 151). 
Another more normal type is well exposed at the Thatcher Road 
bridge a mile south-southwest of the Attleboro station. About forty 
feet of coarse gray, conglomeratic sandstone are exposed in a fine 
glaciated ledge above the railroad. Farther north, at Sheldonville, 
and eastward, the sandstones are deeply colored red. 
——:— Shale. Shales form a large proportion of the Carboniferous 
series in the Narragansett Basin. They occur in varying horizons 
but are most conspicuous in the middle group or the Coal Measures. 
They are frequently carbonaceous and fossiliferous and are accom- 
panied at many localities by beds of coal. They are widely dis- 
tributed throughout the basin but assume greater importance toward 
the southern part. 
——:— Limestone. Two occurrences of limestone are known in the 
Narragansett Basin. The main exposure is found at the south base 
of the hill occupied by the town of South Attleboro. Only six feet 
of sediments appear in the section. The limestone occupies irregular 
kidney-shaped cavities or is found in rude layers or isolated nodular 
masses one-half inch in diameter, frequently elongated parallel to 
the strike, and lies stratigraphically low in the red series. ‘The other 
occurrence is at North Attleboro, where the rock is entirely similar in 
character and mode of occurrence. In both cases the limestone is 
evidently of secondary origin and resembles that of the Norfolk 
Basin (Woodworth, d, p. 149-150). 
——:— Associated Igneous Rocks. In the northwestern part of 
the basin near North Attleboro contemporaneous acid volcanic rocks 
accompany the Carboniferous sediments. The mutual relations of 
voleanics-and sediments are discussed in the succeeding chapter. 
Texture of the Conglomerate. Variations in the texture of the 
conglomerate occur both vertically and horizontally. The coarsest 
conglomerate lies at the top of the series and is preserved only in syn- 
clinal areas. At the junction of Thatcher and County Roads in 
Attleboro, and half a mile south, the upper conglomerate is well exposed. 
The pebbles attain the size of six or eight inches. Farther south, at 
Purgatory and the Paradise Rocks near Newport, the conglomerate 
is much coarser, indicating a gradation in texture in that direction. 
The relation of shape to size, in the case of the pebbles, is not so 
o 
