1875.] 409 [Dodge. 



repeat here the familiar suggestion that similar conglomerates would 

 probably be the result of compacting and hardening influences act- 

 ing on the unstratified masses of pebbly gravel so abundant in this 

 vicinity. Such conglomerates would also, of course, exhibit occa- 

 sional passages to sandstone and slate. 



The materials of the conglomerates may, to a great extent, be 

 traced to the older rocks still preserved in the neighborhood. The 

 form and appearance of many of the pebbles tend strongly to confirm 

 the theory that these early rocks had a glacial origin as well as the 

 recent gravels produced by the later ice action of the commonly so- 

 called " glacial period. " I have already mentioned the occurrence in 

 the conglomerate of the more common kind, of pebbles of older slate. 

 The conglomerates associated with some of the slates of this vicinity, 

 too, are apparently of different character from, and are in some cases, 

 probably, the origin of certain pebbles found in the more abundant 

 variety. The vagueness of this latter expression must not be taken 

 to imply the identity of all the conglomerates I have brought together 

 in this section. The grouping of the conglomerates of these various 

 localities in one system, while probable as an inference, is not sure, 

 owing to the absence of fossils and the insufficiency of lithological 

 character as a test. 



The most probable localities for the determination of the relative 

 ages of the conglomerates and slates at those places are, the eastern 

 shore of Squantum ; in Newton and Brighton (along the Boston and 

 Albany Railroad) near Charles River ; Newton, on Murray Street, 

 north of Otis ; between Auburndale and West Newton ; at the corner 

 of Waverly Avenue and Cotton Street ; the river bank north of 

 Newton Upper Falls on the Newton side, where the slate and con- 

 glomerate are exposed near each other. In Weymouth and Hing- 

 ham, the eruptives, conglomerate and slate seem to be so related that 

 the conglomerate must be more recent than the slate. The conglom- 

 erate has a low dip, while the slates are nearly vertical, and both are 

 cut by the intrusive outflows. The most satisfactory proof on this 

 point would be to find a slate ledge striated by early glacial action 

 under a mass of overlying conglomerate. 



Regarded as a whole, the conglomerates of this northern area, 

 north of slate (J), and their associated slates, dip northerly from 

 nearly horizontal to 45° or more, with a strike of about E. N. E. — 

 W. S. W. The principal system of joints seems to be in N. N. E. — 



