100 BULLETIN: MUSEUM OF COMPARATIVE. ZOOLOGY. 
out into lenticular masses. In its general aspect and composition this 
rock does not resemble those of the Boston, Norfolk, or Narragansett 
Basins. 
The, Woonsocket Conglomerate also occupies a rather limited area 
and is characterized by such a high degree of metamorphism that its 
composition is often not clearly distinguishable.. Here too there is 
little apparent, resemblance to the rocks of the basins east and south. 
Age Relations. The age of the Roxbury Conglomerate has not been 
determined with accuracy. Among its pebbles granitic fragments 
are common. Granite of the Quincy type has been shown by Wads- 
worth to be intrusive into the Braintree slates (b, p. 275), which have 
yielded Middle Cambrian fossils, Paradoxides harlani Green (W. B. 
Rogers, a, p. 27-29, 40-41). Pebbles of another type of granite, whose 
relations to the Quincy granite are not certainly known, are.abundant 
in the conglomerate. Crosby believes the granites in question to be 
differentiation products of a single batholite (n, p. 311 et-seq.).. The 
slates at Hyde Park are cut by granite dikelets and felsite (Crosby, 
p, p- 42) so that the conglomerate which contains pebbles both of 
felsite and of slate must be younger than both. of these rocks. The 
Quincy granite is therefore of later age than the Middle Cambrian. 
The discovery at Forest Hills of what are believed to be fossils has not 
thrown much light on the subject of the true age of the conglomerate. 
The forms in question, as described by Burr and Burke, occur in a 
sandy zone near the top of the conglomerate series. They are cylin- 
drical in form, with circular cross-sections, and are believed to be casts ` 
and moulds of trunks or roots of tree-like forms. The largest has a 
maximum diameter of 4.8 inches and all are marked by somewhat 
irregular transverse wrinklings.. No organic matter is preserved. 
(Burr and Burke, p. 180). The only characteristic features are the 
transverse markings and it is possible that even these may be of mechan- 
ical origin. Assuming organic origin as the most probable explanation 
of these forms they still have no determinative value for they may have 
been derived from Devonian or Triassic as well as from Carboniferous 
life (ibid., p. 181-183). 
Moreover, in the consideration of the age question the possibility 
of the presence of unrecognized upper Cambrian or Silurian rocks in 
the region must be kept in mind, as well as the fact that the formation 
may represent more than one geological period. Nevertheless the 
occurrence of granitic pebbles in such abundance in the conglomerate 
shows that a long interval of erosion must have succeeded the period 
of granitic intrusions, for granite is usually.a deep-seated rock and its 
