222 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
specimens of the rock in question now in the students’ collection of 
the laboratory of advanced geology at Harvard University were not 
satisfactorily identified. While, therefore, the writer is not prepared 
to deny the existence of pebbles of the Blue Hills porphyry in the 
conglomerate of the Norfolk Basin, his observations have not con- 
vinced him of its presence. Moreover, the fact that both along the 
south slope of Bear Hill and at the northwest end of Great Pond the 
conglomerate is broken into large masses that cannot certainly. be 
said to be in situ seems to indicate that the conglomerate is not in 
simple sedimentary contact with the igneous rocks to the north, but 
that a zone of displacement exists along the northern border of the 
sediments. The fact that the southern base of the Blue Hills is bor- 
dered largely by low land occupied by swamps, streams, and ponds 
is not trustworthy evidence but it is at least favorable to the idea of a 
zone of dislocation. 
The Sedimentary Series. The most continuous exposure of the 
beds of the sedimentary series is found in the rocky ridge already 
mentioned, east of the Neponset River. ‘The northernmost expo- 
sures display the giant conglomerate with boulders two and a half feet 
long and one and a half feet wide, accompanied by pebbles eight 
or ten inches in diameter, all somewhat rounded. Outcrops along 
the ridge are frequent for a mile or more south to Pecunit Street and 
show a rapid gradation from the coarse conglomerate through finer 
conglomerates and grits to sandy red slate, showing beautiful cross-bed- 
ding, mud-cracks, and-ripple-marks. According to Crosby the dips 
are steadily southward at angles varying from 70° to 90° (Crosby; 
n, p. 468). The writer's observations, however, show a strike of N 
60°-70° E and a dip varying from a steep northerly, almost vertical 
inclination at the north end of the ridge to 70° or 80° S near the shale 
at the south. The attitude of the ripple-marks and mud-cracks shows 
that the strata are not inverted. East of this ridge the exposures all 
show a tendency to red color but farther to the southwest grayish and 
greenish rocks appear as well. Other scattered groups of outcrops 
occur east of Ponkapoag Pond, north of Canton Junction, at East 
Walpole, and farther southwest toward Wrentham. The most inter- 
esting of these occurrences is to be found in Pierce’s Pasture at Pond- 
ville, described by Woodworth. Here the Carboniferous beds rest on 
hornblende granitite and dip steeply north in the form of a closed and 
puckered syncline, pitching eastward (Woodworth, d, p. 136). The 
basal member of the series here is arkose, which apparently rests upor 
the granitite from which it was derived and which it closely resembles. 
