MANSFIELD: ROXBURY CONGLOMERATE. ` 193 
allied rocks may be changed to gneisses and schists by pressure, the 
rocks becoming plastic. These views were vigorously opposed by 
Jackson and Rogers, who argued that the so-called distorted pebbles 
were only water-worn joint-blocks. The same contest was still con- 
tinued as late as 1880 by Crosby and Wadsworth, the former claiming 
that at certain ledges in Brighton the pebbles showed signs of deforma- 
tion while in a state of plasticity induced by pressure, while the latter 
asserted that the features noted were produced by the glaciation of 
the water-worn pebbles exposed at the surface of the ledges. 
Papers by Hunt in 1870 refer to the sediments of the Boston Basin 
only in a general way. A few years later Dodge contributed two 
important but brief papers on the geology of Eastern Massachusetts. 
Shaler has written several short papers, notably an account of the 
slate exposed in the floor of the Chestnut Hill Reservoir and its rela- 
tions to the overlying conglomerate and a short paper describing the 
Boston and Narragansett Bays as overlapping synclinal troughs, 
faulted down longitudinally and transversely. In his later mono- 
graph on the Narragansett Basin the same writer includes certain 
features of the Boston Basin in connection with his treatment of the 
Rhode Island sediments. 
The most extended and detailed studies of the Boston Basin have 
been made by Crosby, who has written a series of lengthy papers 
which will be referred to later. Briefer papers announcing the dis- 
covery of fossils and discussing the structure of the Newton-Brookline- 
Brighton area have been published more recently by Burr. 
The igneous rocks of the basin have been discussed by a number of 
writers, including Wadsworth, who gives an extended bibliography 
of the geology, mineralogy, and petrography of the basin up to 
1877, Crosby, Benton, Davis, Williams, Diller, Wolff, Miss Bascom, 
Hobbs, Wilson, and Burr. 
Early Views of Crosby. Before the announcement by Wadsworth, 
in 1881, that the Paradoxides slates of Braintree are invaded by granite 
there was much difference of opinion as to the relation of the slates to 
the conglomerates. The question is still open as regards the rocks of 
the Boston Basin proper. In his earlier work (1880) Crosby main- 
tained that all the slate is of the same age, Cambrian, as indicated by 
the Paradoxides beds at Braintree, and that the conglomerate under- 
lies the slate conformably and grades upward into it (b, p. 186). In 
opposition to the view that pebbles of slate occur in the conglomerate, 
he maintained that such is not the case, but that the so-called pebbles 
are either contemporaneous deposits of lenses or pockets of slate in 
