181 



PALEOZOIC FOKMATIONS. 



Like the Shawmut group, the Paleozoic rocks of Eastern 

 Massachusetts occur, as already indicated, only in limited basins 

 or depressions excavated in the ancient crystalline formations. 

 Three of these basins have been recognized, and they are almost 

 as well marked in the modern as in the ancient topography ; for 

 I hold the view that these basins probably existed as such before 

 the deposition of the sediments which they contain. In this 

 connection it is interesting to observe that Messrs. Bailey and 

 Matthew, as one result of their researches in New Brunswick, 

 have found that the Cambrian strata of that Province are con- 

 fined almost entirely to the depressions of the present surface, 

 which probably existed as genuine valleys of erosion, arms of 

 the Gulf of Maine, in pre-Cambrian time. In Newfoundland, 

 too, we find substantially the same relation between these oldest 

 uncrystalline formations and the larger features of the modern 

 topography ; the evidence all pointing to the great antiquity 

 of the latter, where carved from the crystalline rocks. 



The smallest and most northerly of the Massachusetts basins 

 is that now traversed by the River Parker, in Newbury. The 

 second in point of size, and the best known, holds Boston 

 and its environs ; while the third, largest and most southerly, 

 extends from Newport and the western shore of Narragansett 

 Bay, north-easterly through Bristol and Plymouth Counties in 

 Massachusetts, and has been called the Narragansett basin. 

 Near the north-east corner of Rhode Island the last-mentioned 

 basin divides, a narrow branch sweeping first to the north and 

 then to the north-east, through Norfolk County to Braintree, 

 where it nearly, but probably not quite, connects with the 

 Boston basin. All these depressions have approximately the 

 same E.N.E. trend. 



Prof. Shaler^ has described the Boston and Narragansett ba- 

 sins as overlapping troughs ; the first expanding and deepening 



iProc. Bost. Soc. Nat. Hist., xvii., 488. 



