274 



drift ; but their connection in either past or present time seems 

 very improbable because of the unlikeness of the sediments. 

 The rocks of the adjacent portion of the Boston basin, in Brain- 

 tree and Weymouth, it will be remembered, are compact gray 

 slates, including the Paradoxides bed ; while the so-called 

 Devonian strata are mainly of a red color, consisting to a large 

 extent of highly ferruginous slate, sandstone, and conglomerate. 

 The ferruginous character is maintained throughout nearly the 

 entire extent of the formation ; so that these rocks, and 

 especially the slate, may be easily traced by reference to the 

 color alone. The conglomerate is rarely coarse, and consists 

 largely of pebbles of quartz and quartzite, though the other 

 crystalline rocks of that region are also well represented. It 

 is usually less deeply colored than the arenaceous and slaty 

 beds ; these more compact rocks, however, are also often light- 

 colored — grayish or greenish. Thin layers of limestone are 

 included in certain portions of the formation. Endogenous 

 quartz is abundant, veins one to two feet wide sometimes oc- 

 curring. 



With the co-operation of Mr. George H. Barton, I am now 

 (November, 1879) engaged in a systematic survey of this 

 elongated arm of the Narragansett basin, which Mr. W. W. 

 Dodge has appropriately designated the Norfolk County basin. 

 Our work is only fairly begun ; and, therefore, since my pre- 

 vious observations on these rocks have been few and casual, it 

 seems wise not to attempt detailed descriptions of the lithology 

 and stratigraphy of the belt here. For the best that has yet 

 been done in this direction we are indebted to President Hitch- 

 cock l and Mr. Dodge. 2 



It is not difficult to conceive under what conditions the rocks 

 of the Norfolk County basin were probably deposited. This 

 geologic valley is narrow ; and, judging by the present disposi- 

 tion of the uncrystallines of Rhode Island and Southern Massa- 

 chusetts, it has always been well shut off from the open sea. 



1 Final report on the Geology of Massachusetts. 

 2 Proo. Bost. Soo. Nat. Hist., xvn., 411 et seq. 



