268 



small, closed synclinals, having the axial planes inclined to the 

 north. It would be possible, however, to account for all the 

 structural phenomena observed, by means of strike faults with 

 the downthrow on the south ; and in some respects this is the 

 the more probable view. 



Slate is the prevailing rock, and such conglomerate as occurs 

 is invariably fine-grained and slaty, the formation including no 

 coarse materials. It is practically impossible to make out in 

 any of the numerous patches of these rocks any definite strati- 

 graphical relation between the conglomerate and slate ; in fact, 

 this is essentially a slate formation. 



I have seen no clear indications that any part of the amyg- 

 daloid is exotic, while the absence of special alteration in the 

 slate points to the contrary conclusion. The slate makes 

 its first appearance on the east bank of Little River, near its 

 junction with the River Parker. It is here very fissile, and in 

 part of a dark green color, and decidedly chloritic. The same 

 slate forms both banks of this tributary at its mouth. On 

 Kent's Island the rocks in question are confined mainly to the 

 southern-central portion. The schistose conglomerate is well 

 exposed on and near the railroad. West of Kent's Island these 

 rocks are visible near the Newburyport Turnpike ; but beyond 

 this there are no actual outcrops, although we have abundant 

 evidence, in the shape of erratics, of their farther extension in 

 this direction for a mile and a half, or nearly to Byfield, follow- 

 ing the general course of the river all the way. These erratics, 

 which are very numerous along the road on the south side of 

 the river, are all of a highly ferruginous, arenaceous slate ; a 

 plain indication that this basin has always been narrow and 

 land-locked ; and it is probable that the ancient shore line ex- 

 tended but little beyond the present limits of the deposits. 

 The uncrystallines of this basin are almost identical with those 

 in the vicinity of South Natick and Charles River Village, and 

 were probably deposited under similar conditions ; the adjoin- 

 ing crystallines, the sources of the sediment, are also the same 

 in the two regions. 



