walcott.J EASTERN MASSACHUSETTS. 73 



111 1S32 Prof. Edward Hitchcock 1 described the argillite in the vicin- 

 ity of Boston, and stated that the unstratified rocks were of igneous 

 origin and intrusive among the stratified rocks. A general description 

 of the argillite is given in the text with localities, and on the map the 

 geographic distribution, as known to him, is delineated. This includes 

 the Quincy locality. In the final report of the Massachusetts survey 

 Dr. Edward Hitchcock, in speaking of the argillaceous slate of the east- 

 ern part of the State, says that owing to its intimate connection with vari- 

 eties of rock referred to the Graywacke group it ought to be described 

 as one of the members of it, although marked as a distinct deposit on the 

 map. He considered this slate as older than the graywacke, because 

 fragments of the slate occur in one of the varieties of conglomerate of 

 the graywacke. 2 On the same page, in describing the limestone in the 

 southwest part of Attleborough, he says small beds of compact light 

 gray limestone occasion the red sandrock. He did not see much of it 

 in place, but the numerous blocks in the stone walls indicated its ex- 

 istence in that locality. On the map accompanying the report the ar- 

 gillaceous slate is shown in eastern Braintree, the central part of Quincy, 

 and thence extends across. Milton and Dorchester to Roxbury. A small 

 outcrop is also indicated on the north side of Nahant. The North At- 

 tleborough locality of the Cambrian as now known is covered by the 

 Carboniferous (No. 17 of the legend of the map). The description in 

 the report of 1841 is essentially the same as in the preliminary report of 

 1833. 



In an article on the crystalline limestones of North America Dr. T. 

 S. Hunt 3 suggests that the limestones interstratified with the red slates 

 at Attleborough, as described by Dr. Hitchcock, may correspond to 

 those which with similar slate and sandstone are met with at the base 

 of the Carboniferous formation in Canada and in New Brunswick. 



The long silence in relation to the geologic age of the altered rocks 

 of eastern Massachusetts in the vicinity of Braintree was finally broken 

 in 1856 by the announcement of Prof. W. B. Eogers that trilobites of 

 the genus Paradoxides had been discovered at a quarry in a belt of 

 siliceous and argillaceous slate lying on the boundary of Quincy and 

 Braintree, about 10 miles south of Boston. In announcing this discov- 

 ery he compares the species found with Paradoxides spinosus of Bar- 

 rande. He states: 4 



The rock in which these fossils occur is a compact, dense, rather fine-grained, sili- 



co-argillaceous slate or slaty sandstone, containing little or no carbonate of lime. 



* * One of the most curious facts relating to the trilohite of the Quincy 



and Braintree belt is its seeming identity with Paradoxides harlani, described by 



Green in his Monograph of North American Trilobites. 



'Report on the geology of Massachusetts, examined under the direction of the government of that 

 Stat<> during the years 1830 and 1831. Am. Jour. Sci., vol. 22, 1832, pp. 1-70, with map. 



2 Final report on the geology of Massachusetts, 1841, vol.2, p. 537, Amherst. 



3 A m. Jour. Sci., 2d ser., vol.18, 1854, p. 199. 



4 Proofs of the Protozoic age of some of the altered rocks of eastern Massachusetts from fossils 

 recently discovered. Am. Acad. Proc, vol. 3, 1856, p. 317. 



