76 THE CAMBRIAN. [Bvth.it 



rocks of Braintree and St. John, New Brunswick, to the subjacent 

 crystalline Huronian strata. 



The following year Prof. W. O. Crosby described the Geological Map 

 of Massachusetts, and said: 1 



Although the fossils characteristic of the Acadian group have been found at only 

 one locality in Massachusetts, viz, Hayward's quarry, in Braiutree, yet most observ- 

 er agree that the greater portion of the slates in the vicinity of Boston are probably 

 of Primordial age ; and I have so represented them on the map. 



The strata referred to are then described in a general way. 



In 1875 Prof. W. B. Rogers 2 announced the discovery of impressions 

 suggestive of the fossil Lingula mentioned by him from Fall River, in 

 pebbles of the conglomerate, at Newport, Rhode Island. The pebbles 

 consist of a gray siliceous rock or qnartzite. 



The memoir of Prof. W. O. Crosby on the Geology of eastern Massa- 

 chusetts, with its accompanying map, appeared in 1880. He says: 3 



The Paleozoic rocks of eastern Massachusetts occur, as already indicated, only in 

 limited basins or depressions excavated in the ancient crystalline formations. . . . 



The most diligent search, continued for many years, by, in the aggregate, a small 

 army of observers, has failed to bring to light, among the rocks of the Boston Basin, 

 more than one locality affording fossils. This is the celebrated slate quarry of the 

 south shore of Hayward's Creek, in the extreme northeast corner of Braintree. 



Prof. Crosby 4 concludes that the Paradoxides bed in Brain- 

 tree is the established base line for the stratigraphy of the Boston 

 Basin ; and that all the rocks in the Boston Basin above the Shawmut 

 group, and including the Paradoxides bed, belong to one and the same 

 essentially conformable series; although (p. 18G) there is in the Boston 

 Basin essentially but one conglomerate and one slate, and the former 

 underlies the latter. From this it follows that the slate is of Primor- 

 dial age, and the conglomerate must be of the same age, or older. The 

 conglomerate is stated to pass gradually into the slate, and a detailed 

 description of these two formations is given as they occur in the Boston 

 Basin. On the map a part of Nab ant is colored to indicate the Cam- 

 brian slate. In the text he describes white and gray limestones that in 

 texture are very compact and highly crystalline or saccharoidal. These 

 have a thickness collectively of perhaps 20 feet. He assigns to the 

 conglomerate a maximum volume not exceeding 1,000 feet; and con- 

 siders that the greatest thickness of the slates cannot be much less than 

 that of the conglomerate, though in some cases falling below 500 feet. 5 



Dr. M. E. Wadsworth, 6 in discussing the relation of the Quincy gran- 

 ite to the Primordial argillite of Braintree, states that Dr. Hunt was 



1 Report on the geological map of Massachusetts, Boston, 1876, p. 40. 



s On the Newport conglomerate. Boston Soc. Nat. Hist., Proc, vol. 18, 1875, p. 100. 



3 Contributions to the geology of eastern Massachusetts. Boston Soc. Nat. Hist., Occasional papers, 

 No. 3, 1880, p. 181,183. 



4 Op. cit., pp. 184, 185. « Op. cit. , p. 2G6. 



6 On the relation of the Quincy granite to the Primordial argillite of Braintree, Massachusetts. 

 Boston Soc. Nat. Hist., Proc, vol. 21, pp. 274-277, 1882. 



