MANSFIELD: ROXBURY CONGLOMERATE. 101 
exposure to pebble-making agencies suggests the removal of a heavy 
sedimentary covering. This consideration, together with the close 
resemblance of the Boston Basin sediments to the rocks of the Norfolk 
and Narragansett Basins, in which undoubted Carboniferous fossils 
have been found, have led many geologists to believe that the Roxbury 
Conglomerate is also of Carboniferous age. 
In the Norfolk Basin casts of tree trunks have been described by 
Crosby and Barton and by Woodworth as occurring near Pondville, 
Mass. (Crosby and Barton, p. 416-420; Woodworth, b, p. 145). The 
writer too has found irregular cylindrical cavities, unlike pits formed 
by the removal of pebbles from the conglomerate and comparable to 
casts made by irregular stems or roots of plants. The forms referred 
to occur in a gritty zone in a ledge about 200 yards southwest of the 
residence on the top of the ridge, a mile south of the intersection of 
Green Lodge Street with the eastern side of the Neponset valley. One 
of the supposed fossils is exposed on the front of the ledge and measures 
two feet in length with a breadth and depth of three and five inches 
respectively. The front part of the cast is broken away and the 
inside is marked by transverse wrinklings after the manner of the 
fossils found at Forest Hills. In this case, however, it is not certain 
whether the markings are original impressions or only due to weather- 
ing along the shear planes which cut obliquely across the cavity. The 
wrinklings are not well developed on the north side. The other 
supposed cast is found on the top of the same ledge. A hole two or 
three inches in diameter with somewhat elliptical cross-section was 
dug out with a knife to the depth of six or eight inches without showing 
any diminution in size or any bottom. The shape of the cavity is 
irregular and unlike that of any of the pebbles seen in the rock, but is 
such as might well be expected in the cast of a root or somewhat irregu- 
lar stem. Both forms lie in the plane of the bedding, which is here 
nearly vertical, and they must have been practically horizontal at the 
time of their deposition. Well-defined Carboniferous fossils, however, 
have been found by Woodworth toward the southern part of the basin 
in the railway cut north of Canton Junction (Woodworth, b, p. 146). 
In the Narragansett Basin beds of coal occur at several localities 
and a number of insects and plants have been identified. Some of 
these have been compiled and tabulated by Woodworth in his report 
on the northern part of the basin (d, p. 202-204). From a study of 
the flora of the Rhode Island coal measures Lesquereux concluded 
that the latter were equivalent to beds of the Upper Carboniferous in 
Pennsylvania (ibid., p. 204). 
