62 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



belong to the genus Calamites, and the whole series is assigned with little doubt 

 to the Carboniferous. The similar series in the Worcester district comprises the 

 Oakdale quartzite below and the Worcester phyllite above. The Worcester 

 phyllite is Carboniferous, for it contains Lepidodendron and several species of 

 ferns at the Worcester 'coal mine.' Its substantial equivalence to the Rhode 

 Island formation is indicated not only by its fossils but by beds of graphitic 

 anthracite it includes. The lower parts of the series in the two areas also exhibit 

 many points of resemblance, but in the Narragansett Basin the lower part is 

 made up chiefly of conglomerate with subordinate sandstone and in the Worcester 

 district almost wholly of sandstone with only a little conglomerate. It has 

 generally been maintained that the conglomerates were derived from higher land 

 lying to the east, and, on the assumption that most of southeastern New England 

 was once covered by Carboniferous strata and that the rocks of the several basins 

 were, therefore, originally continuous, this would explain the finer grain of the 

 Oakdale quartzite lying to the west." 



(Page 1 86.) "After the irruption of the Devonian (?) igneous rocks there 

 was a long period of quiesence and erosion, during which the region was so greatly 

 denuded that large areas of those rocks were exposed at the surface and deeply 

 weathered. Early in Carboniferous time, as nearly as can be determined, another 

 period of eruptive activity began and lasted, in one form or another, until after 

 the close of the deposition of the Carboniferous strata." 



(Page 51.) "The coarse Dighton conglomerate, spread in great sheets over 

 the thick coal-bearing shales of the Rhode Island formation in the Narragansett 

 Basin, presents problems of its own. It is coarser toward the south and the 

 pebbles of fossiliferous Upper Cambrian quartzite, not known in place, for which 

 the rock is famous, are also larger and more abundant toward the south. On the 

 other hand, pebbles composed of muscovite granite are larger and more abundant 

 toward the north. To explain such conditions, Mansfield' assumed the former 

 existence of mountains of Alpine height on the southeast, which may have been 

 the source of the floods and glaciers and have supplied the coarse material. 

 Other mountains on the northwest of the Boston district were assumed as a source 

 of the muscovite granite, as the nearest known granite of that sort lies in that 

 direction. It is now known, however, that the muscovite granite northwest of 

 Boston is younger than the Carboniferous sediments. The Dighton conglomerate 

 finds its possible equivalent in the conglomerate at Harvard, in the Worcester 

 district." 



(Page 58.) "Correlation and age of the formations: No fossils, except at 

 one locality a few obscure tree trunks, possibly Cordaites, have been found in the 

 Roxbury conglomerate and none in the Cambridge slate. The age of the beds 

 is assumed from what appear to be the most reasonable correlations with the 

 formations of the Narragansett Basin, on the south. In both basins volcanic 

 eruptions of similar lavas occurred during the early stages of deposition and 

 presumably at about the same time. The Ro.xbury conglomerate is believed to 

 be equivalent to the formations of the Narragansett Basin as a whole, and if so, 

 it ranges in age from early Pennsylvanian possibly to Permian." 



Emerson" believes that the Carboniferous deposits were of continental 

 formation and that the disconnected areas now forming the several basins 



1 Mansfield, G. R., The Origin and Structure of the Roxbury Conglomerate, Harvard 



College Museum of Comparative Zoology Bulletin, vol. 49, pp. 99-271, 1906. 

 '^ Loc. cit., p. 52. 



