italcott.] EASTERN MASSACHUSETTS. 77 



mistaken in regarding the granite as of Hurouiaii age, as was Prof. Shaler 

 in regarding it as a metamorphosed sedimentary rock. He says the 

 argillite is surrounded by intrusive granite of a later age, thus adopt- 

 ing the view advanced by Dr. Hitchcock in 1832. In describing the 

 slates, he says they dip a little west of south at an angle of 55°, nearly 

 as given by Mr. Lea. He thinks that, judging from their writings, Profs. 

 Eogers and Shaler based their conclusions regarding the dip of the 

 argillite upon its structural character. In another paper, published 

 the following year, Dr. Wadsworth discusses the argillite and conglom- 

 erate of the Boston Basin, 1 and concludes from studies made by him that 

 there are at least two distinct argillites. One like that underlying the 

 conglomerate on Beacon street, Boston, and resembling in some of its 

 characters the Paradox ides argillite at Braintree. The second is of 

 coarser grain, often more decidedly arenaceous, and generally of a gray, 

 Mack, or reddish color, and forms the Somerville argillites (" Cam- 

 bridge slates.") It is stated : * 



So far as we have any evidence at present the oldest surface rocks in this basin 

 are the argillites and the schists of allied character. Of these we only know the age 

 of a very small area in Braintree and Quincy. * * * Older rocks than the Brain- 

 tree (Paradoxides) argillites may exist, but of their existence we thus far have no 

 proof. 



The discovery of fossils of Lower Cambrian age near North At tic- 

 borough, Bristol County. Massachusetts, by Prof. N. S. Shaler, 3 located a 

 second area of Cambrian rocks iu eastern Massachusetts. He describes 

 the geographic distribution and the character of the rocks, and in an 

 accompanying paper in connection with Mr. A. F. Foerste gives a descrip- 

 tion of the fauna. As the description of the strata and the fauna 

 is that which is given in our summary of the present knowledge of the 

 rocks of eastern Massachusetts, it is here omitted. 



In a review of the stratigraphic position of the Olenellus fauna by 

 Mr. C. D. Walcott inl889, 4 it is shown that the Paradoxides fauna of 

 Braintree, Massachusetts, of St. John, New Brunswick, and of south- 

 eastern Newfoundland, is superjacent to the Olenellus fauna, and thus 

 above the Olenellus fauna as found at North Attleborough by Prof. 

 Shaler. This is presented more fully iu a paper in the Tenth Annual 

 Ileport of the Director of the U. S. Geological Survey. 5 



In a sketch of the physical history of the Boston Basin, Prof. W. O. 

 Crosby 6 mentions the old and more or less altered or metamorphic slates 

 of the Braintree quarry, and states it to be clearly established that the 



'The argillite and conglomerate of the Boston Basin. Boston Soc. Nat Hist., Proc., vol. 22, 1883, 

 pp. 130-133. 



2 Op, cit., pp. 132,133. 



3 On the geology of the Cambrian district of Bristol County, Massachusetts. Bull. Mus. Comp. 

 Zooi. Harv. College, vol. 16, 1888, pp. 13-26. 



4 Stratigraphic position of the Olenellus fauna in North America and Europe. Am. Jour. Sci., 3d 

 ser., vol. 37, 1889, pp. 374-392 ; vol. 38, 1889, pp. 29-42. 



6 The fauna of the Lower Cambrian or Olenellus zone. 10th Ann. Rep. U. S. Geological Survey, 1890, 

 pp. 509-763, plates 49-98. 



6 Physical History of the Boston Basin. Lowell free lectures, 1889-1890. Boston, 1889, pp. 22. 



