64 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
manner toward the east, for the conglomerate ridges disappear, and the 
Chestnut Hill Slate belt apparently becomes continuous with that to 
the north. 
That faulting of the overthrust type is to be looked for in the region 
is Shown by the occurrence of a second thrust crossing Commonwealth 
Avenue at Summit Street, half a mile north of the one described 
(Plate 2, Loc. 22). This is well shown in exposures on both sides of 
the avenue. The slate is here repeated, lying on top of the conglomer- 
ate and again overthrust by conglomerate to the north. The outcrop 
on the east side of the street shows particularly well the way in which 
the conglomerate has been crumpled by dragging on the plane of the 
thrust. This fault is seemingly not traceable westward. Toward the 
east it is complicated by a normal fault of later date. 
The discontinuity of the Chestnut Hill slate belt, the actual occur- 
rence, in two instances, of faulting on the contact between the slate and 
the conglomerate, the general discordance in structure between the two 
rocks and the known occurrence of a fault bringing about similar rela- 
tions a short distance to the north, all point to the same conclusion, that 
the conglomerate has been thrust over the slate. All of these facts are 
very difficult to explain on the supposition that the conglomerate passes 
in a syncline beneath the slate. 
The stratigraphic succession shown in this conglomerate belt is not 
such as to indicate anticlinal structure. South of the melaphyr the 
rocks are prevailingly conglomerate, coarse, as a rule, but becoming 
finer toward the igneous rock. Near the melaphyr sandstone bands 
are frequent, and there are occasional interbedded slaty layers. This is 
the character of the upper portion of the conglomerate in the adjacent 
Brookline area and quite unlike the massive beds in the lower zones. 
The sediments in actual contact with the melaphyr are seldom coarser 
than sandstone. In the eastern extremity they are prevailingly slates. 
Such rocks are out of place at the base of the sedimentary series, judg- 
ing from the evidence elsewhere. North of the melaphyr, outcrops are 
few. The greater number are of slate. Thin conglomerate bands occur 
in a number of places in association with finer sediments. In two lo- 
calities, only, are these conspicuous. A bed of conglomerate, perhaps 
thirty feet in thickness, is exposed on North Beacon Street, Brighton. 
It conforms in dip and strike to the slates on the north and on the 
south, and is apparently interbedded with them. Similar beds of con- 
glomerate are known to occur within the slate series in other parts of 
the region. Conglomerate is exposed in a cutting near the Boston and 
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