200 BULLETIN: MUSEUM’ OF COMPARATIVE ZOOLOGY. 
westward near the Charles River. Crosby interprets the structure 
as a syncline closely folded and wedging out westward. Towards 
the east he believes that the syncline broadens as it approaches Boston 
Harbor. He recognizes the thrust faulting at Chestnut Hill Reser- 
voir and at Newton Center but considers these dislocations merely 
as interruptions of the syncline. (Crosby, g, p. 11). Burr, on the 
other hand, considers the faulting as the main feature, though he 
recognizes the possibility of synclinal tendencies at Chestnut Hill 
(Burr, b, p. 63). He states emphatically that there is no swinging of 
strikes at the west end of the slate belt to indicate synclinal struc- 
ture (ibid., p. 65). He believes that the fault dies out westward, for 
at Newton Lower Falls fine conglomerate such as usually occurs 
immediately beneath the slate appears, as if the throw had not been 
sufficient to bring up the lower members of the conglomerate. East- 
ward, too, he thinks the fault dies out, for the conglomerate ridges 
disappear in that direction (ibid., p. 63-64). The latter supposition 
does not, however, necessarily hold, since a general eastward pitch of 
the axes of the conglomerate would carry the latter below the slate 
in that direction. With slate on both sides of the fault the deter- 
mination of the latter would be difficult. 
——:—The Savin Hill-Brookline Conglomerate. A broad conglom- 
erate area extends from Savin Hill through the northern part of Dorches- 
ter, Roxbury, West Roxbury, Brookline, and Newton to the Charles 
River. On the north it dips beneath the narrow slate belt just de- 
scribed and on the south it also passes below the slate, with which it 
appears to be entirely conformable. The northerly dips are relatively 
gentle, usually not exceeding 20°-30°, but the southerly dips are steeper; 
amounting to 60° or 70°. Thus the conglomerate in this zone forms 
a broad and flat-topped anticline, somewhat unsymmetrical, with the 
steeper dip toward the south (Crosby, g, p. 9-10; Burr and Burke, 
p. 183). The conglomerate in this area is abundantly exposed and 
the stratigraphic relations are fairly clear. On account of the decrease 
in size of the pebbles from Brookline to Savin Hill it is believed by 
Crosby (b, p. 234-235) that the latter beds represent higher members 
of the series and that therefore the axis of the anticline pitches east- 
ward. The general disappearance of the conglomerate beneath the 
slate in that direction leads to the same conclusion. It may be re- 
marked, however, as noted by Crosby (loc. cit.), that diminution in 
size of pebbles does not necessarily imply a higher horizon, since it 
has been shown that this feature of a conglomerate may mean simply 
a greater distance from the source of supply. 
