Dodge.] 398 [February 3, 



others of later date, other pudding-stones and slates which, I think, 

 can be identified with another extensively developed member of the 

 group. Yet these several strata, which in some places lie in great 

 masses by themselves, appear in other places to be promiscuously in- 

 termingled, and here the deficiency of lithological character as a dis- 

 tinction, makes itself felt. Conglomerates pass into slates, which 

 closely resemble others which they seem to overlie unconformably 

 elsewhere, and contain portions of, as pebbles. And the outcrops 

 are often so small and few in the basins, and the basins are separated 

 by such extensive areas of the older crystalline rocks, that it would be 

 almost as unsafe to attempt to make out a correspondence between 

 apparently similar strata in the different basins of this vicinity, as 

 between these and the strata of foreign localities. So that an argu- 

 ment on lithological grounds can scarcely be extended from one of 

 these small areas to another. 



It will be seen that beside the small area at Newbury, and the 

 large one occupying portions of Rhode Island, and Bristol and Ply- 

 mouth Counties in Massachusetts, there are in this more immediate 

 vicinity, three somewhat clearly defined basins of these include'd 

 stratified rocks. They are so closely locked in among the crystallines 

 that it seems clear that large quantities in the form of less protected 

 anticlinals must have been removed by denudation, and that small 

 basins may yet be found elsewhere within the areas and among the 

 folds of the more durable subjacent rock. 



Of these three, the largest, which by way of a harmless designa- 

 tion, may be called the Boston basin, occupies all the country between 

 the two bounding lines of crystallines already given, which have their 

 eastern ends respectively at Lynn on the north and Quincy on the 

 south. Its width, accordingly, is about thirteen miles. On the west 

 it is broken into by several projecting ridges of the underlying crys- 

 tallines, and eastward it loses itself under the water of Massachusetts 

 Bay, appearing irregularly in islands and ledges at intervals across 

 Boston Harbor. 



The second, closely resembling the first in its rocks, lies along the 

 north side of the Moose Hill crystalline range, from Cohasset to 

 Braintree, and is open to the harbor on the north. This I will call 

 the South Shore basin. 



The third is long and narrow, curving at about the middle of its 

 length, and tapering to either end ; the eastern near the last men- 

 tioned basin at Braintree, and the southern where I have not yet 





