MANSFIELD: ROXBURY CONGLOMERATE. 165 
Dighton Conglomerate as exposed at Attleboro and in the Seekonk 
and Purgatory Conglomerates the pebbles are often eight or ten inches 
in their greatest dimensions. In the latter rock the pebbles exceed 
one foot in length and one specimen noticed by the writer measured 
nine feet in length. It is worthy of note that the coarsest conglomer- 
ate occurs at the southernmost limit of the exposed portion of the 
basin. 
The pebbles are usually subangular or even rounded but in the 
basal conglomerate described by Foerste some of the pebbles are said 
to be angular (Foerste, b, p. 253). In some of the pebbles in the upper 
conglomerate at Attleboro re-entrant angles produced by intersecting 
joint planes have not been removed by abrasion. 
No striations that could be attributed to glacial action were found 
on any of the pebbles examined but pressure striations and other evi- 
dences of dynamic metamorphic action were seen in a number of in- 
stances. The most remarkable.cases of this kind were observed in 
the pebbles from Fogland Point on the east shore of Narragansett 
Bay. The rock is highly schistose. The pebbles have been flattened 
and stretched into spindle-shaped forms with rounded sides and ends, 
the elongation in many cases amounting to as much as 50 per cent or 
more of the original longer axis. The pebbles have been indented 
and sliced and sets of V-shaped tension cracks have been produced, 
some of which pass entirely through the pebbles. The pebbles thus 
deformed are chiefly gray quartzite but it is not known whether the 
latter corresponds to the fossiliferous quartzite at Newport. In some 
of the specimens examined by the writer the cracks developed in the 
pebbles looked as if they might have originated in the casts of fossil 
Oboli. Another striking instance of deformed pebbles is seen in the 
Purgatory Conglomerate. There the process has not been carried 
quite so far as at Fogland Point but the stretching and shearing have 
been intense. Plates 3 and 5 show field occurrences of the conglomer- 
ate at these localities. 
Color. The color of the conglomerate is usually gray with 
some greenish or purplish tints. Specimens from the northern part 
of the basin often show reddish tones of greater or less intensity. 
——:— Bedding. No well-defined arrangement of pebbles or bed- 
ding of the conglomerate was shown in the hand specimens. Field 
observations will be given later. 
——:— Relations to Igneous Rocks. No specimens illustrating the 
relations of the sedimentary series to the igneous rocks of the basin are 
at hand. Woodworth has described the occurrence of diabase and 
