114 



the diorites, must leave the limestone almost unchanged. The 

 latter rock may be folded and faulted, and may become more 

 or less crystalline, but it is practically infusible. These lime- 

 stone beds have been preserved intact in substantially the 

 same manner as the isolated masses of quartzite already de- 

 scribed. Regarding the limestone as of sedimentary origin, the 

 wonder is, not that the bedding is not more perfect, but that it 

 is not wholly obliterated, and this is explained by the refractory 

 nature of the rock. The Devil's Den and Basin are about half 

 a mile apart, and the line connecting them seems to run a little 

 more northerly than the strike of the deposits, which have not 

 been stratigraphically united, though there is little doubt that 

 originally they formed one continuous bed. An observation 

 recorded in Prof. Hyatt's notes is of special interest in this 

 connection. He found a ledge of crystalline limestone about 

 one-third of a mile south of the city of Newburyport, and on 

 the general line of strike of the Newbury deposits. From the 

 Devil's Basin this ledge is distant, probably, about one mile. It 

 is not shown on the map, and the other deposits are repre- 

 sented as one on account of their nearness and the small scale of 

 the map. The occurrence of the Eozoon canadense in the 

 Newbury limestone has been noticed, ante, p. 25. The siderite 

 mentioned above as associated with the limestone, is found only 

 at the Devil's Basin, and appears to be the same with that 

 characterizing the adjacent granite and diorite. Indeed, I 

 regard this mineral as going far to prove the connection of 

 these various rocks. In the first place, it does not occur in the 

 form of veins, but, as previously stated, is diffused through the 

 rocks almost as a regular constituent ; and in its composition 

 again we have evidence pointing to the same conclusion, for the 

 siderite not only appears to be the same, whatever its associa- 

 tion, but analysis also proves its essential identity with the 

 limestone itself. Following is an analysis, made by Professor 

 Hitchcock, 1 of the siderite occurring in the granite immedi- 

 ately north of Kent's Island : — 



1 Final Report on the Geol. of Mass., p. 191. 



