232 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
The highest member of the series is the Dighton Conglomerate, 
1,000 to 1,500 feet thick, consisting mainly of coarse quartzite and 
granitic pebble. conglomerates, with finer conglomerates and sand- 
stone. 
In the southern area the basal beds present the same general char- 
acteristics as those given for the Pondville group. The Wamsutta 
group, however, is not traceable south of Providence. It is probably 
represented by lower strata of the Kingstown series of Foerste. The 
Kingstown series, consisting mainly of sandstones and conglomerates, 
with coal shales, and the Aquidneck shales of Foerste, composed 
chiefly of shales with coal beds, when traced northward, appear to 
form equivalent sections beneath the Dighton group, one on the 
eastern, the other on the western side of Narragansett Bay. Both 
extend downward to the basal beds. The Purgatory Conglomerate 
forms the upper member of the Carboniferous series in the southern 
part of the basin. It consists mainly of coarse quartzite pebbles, 
usually much elongated and indented (Plate 3, B). It is probably, 
but not certainly, identical in all parts of the field, lying in synelines 
above the coal measures. 
Attleboro GtMeadow Hil/ Swansea 
syncline Syncline syncline 
Fira. 9.— Outline of the structure of the Narragansett Basin (after Shaler et al., 
p. 27). 
General Structure and Thickness. The structure of the Narra- 
gansett Basin has been carefully worked out by Woodworth and 
Foerste in their monograph. In the present paper the intention is 
to give only the main outlines as indicated by them and by the accom- 
panying report of Shaler. The broader structural features are rela- 
tively simple and consist of a system of folds with their axes parallel 
to the borders of the basin. There are three main synclines in which 
the Dighton group appears, the Attleboro syncline on the north, the 
Great Meadow Hill trough through the middle of the basin and the 
Swansea syncline on the south. The central syncline is nearly sym- 
metrical, with relatively low dips, while the synclines parallel with 
it on the north and south have their axial planes inclined away so that 
