74 THE CAMBRIAN. [bull. 81. 



He adds farther: 



The occurrence of well preserved fossils among rocks so highly altered and so con- 

 tiguous to great igneous masses as are the fossiliferous slates of Quincy may well 

 encourage us to make careful search in other parts of New England where heretofore 

 such an exploration would have been deemed useless. 1 



Prof. Louis Agassiz, in commenting upon the announcement of Prof. 

 Rogers, said that, geologically speaking, its importance could hardly 

 be overestimated. We have now, he remarked, a standard level upon 

 which to build up the formation of the met amorphic rocks. 2 Prof. 

 Rogers also communicated the knowledge of the discovery of the 

 Braintree fossils to Prof. J. D. Dana, in a letter dated August 13, 185G. 3 

 He states that his attention was called to the locality by Peter Wain- 

 wright, Esq., who resided in the vicinity of the quarry. 



Dr. Isaac Lea 4 visited the Braintree quarry, and iu reporting upon it 

 to the Philadelphia Academy of Natural Sciences stated that he 

 agreed with Prof. Rogers in placing this formation among the more 

 ancient of the Paleozoic periods. " It lies directly on the granite rocks, 

 or rather it is squeezed in, and is embraced by these rocks (on the east 

 and west sides), which are disturbed by an upheaval." He considered 

 the trilobite found there to be undoubtedly the same as described by 

 Prof. Green many years before under the name of Paradoxides harlani. 



Prof. W. B. Rogers again called attention to the Braintree locality 5 

 for the purpose of noting the fact that the formation was among the 

 oldest of the Paleozoic series, and situated somewhere about the level 

 of the Primal rocks (Potsdam sandstone and the Protozoic sandstone 

 of Dr. D. D. Owen), containing Dikellocephalus in Wisconsin and Min- 

 nesota. 



In 1856 Prof. 0. T. Jackson 6 described the rock at Braintree as a 

 blue gray, argillaceous slate, containing silicate of lime but no carbonate, 

 and some disseminated iron pyrites. The stratification of the rock, as 

 indicated by its grain and cleavage, dips to the north 50°, and runs east 

 and west. The existence of the genus Paradoxides in the argillaceous 

 slates of Braintree, proves them to belong to the lowest of the fossiliferous 

 Silurian rocks, and he believed them to be the geological equivalents 

 of the argillaceous slates of Sweden, which are in a similar manner dis- 

 rupted by the intrusion of syenite. 



1 Am. Acad., Proc. vol. 3, 1856, p. 318. 2 Ibid., p. 319. 



3 Discoveryof Paleozoic fossils in eastern Massachusetts. Am. Jour. Sci., 2d sor., vol.22, 1856, pp. 

 296-298. 



4 [On the trilobite formation at Braintree, Massachusetts.] Phila. Acad. Sci., Proc, vol. 9, 1858, 

 p. 205. 



6 [On trilobitos from Braintree and on the geologic relations of the district.] Boston Soc. Nat. 

 Hist., Proc, vol. 6, 1856, pp. 27-29, 40, 41. 



• [On the Braintree argillite and its trilobites.] Boston Soc. Nat. Hist., Proc, vol. 6, 1856, pp. 42-44, 



