THE CHESTER AMPHIBOLITE AND SERPENTINES. 83 



be found just opposite a shoddy mill near the river, runs in a great curve 

 N. 30° W., so that the serpentine encroaches still more on the ainphibolite 

 and at last occupies nearly its whole width. An inspection of the map 

 (PI. XXXIV) shows that the course of the river, where it separates ser- 

 pentine and amphibolite, is in southward continuation of this curve, and 

 that the serpentine is lodged as a great lens, a mile and a half long and 

 nearly a half mile wide, in the amphibolite. The boundary line between 

 the two runs up the hillside in a narrow gorge, its bottom everywhere 

 encumbered with bowlders, and the amphibolite and serpentine could not 

 be found nearer each other than 10 feet. At that distance there was no 

 trace of ti-ansition from one into the other. Search was made for the bound- 

 ary between the serpentine and the sericite-schist on the east for a mile 

 north through the dense woods, but they could not anywhere be found in 

 actual contact. The contact line was, however, a straight one, following 

 the line of strike of the schist, while the schist, oi-dinarily a very flat-fissile 

 rock, was for all this distance, and, indeed, for the full length of the ser- 

 pentine lens, and in a thickness of above 350 feet, thrown into the most 

 extreme contortions and twistings, the like of which I have hardly seen 

 among any of the rocks of the region. This I take to be another indication 

 of the formation of the serpentine before the final folding of the region. 

 It is likewise interesting that along this line the serj^entine was in many 

 places, and it seemed continuously, separated from the sericite-schists 

 above by a thin layer of amphibolite, and the serpentine, when traced to 

 within a single foot of this, was complete serpentine. The mass of the latter 

 would seem to be, then, strictly speaking, inclosed in the amphibolite. 



As already noted by President Hitchcock, this serpentine mass shows 

 abundant signs of stratification, and I may add that this not only agrees 

 with the dip and strike of the adjoining amphibolite, but shows closer agi-ee- 

 ment still with the latter, extending to the exact thickness of the laminse, 

 the angles and distance of the jointing, etc.; and further, that this structure 

 is one brought out in the serpentine again only by the action of atmospheric 

 agents, below the surface the serpentine appearing wholly compact. The 

 serpentine is the common rather light oil-green variety, and, especially 

 where a fine splintery fracture is developed, it has a dry grayish-green 

 color. It weathers to a deep red brown, and the great ragged hill, bare of 

 vegetation and covered with an almost unbroken layer of immense bowlders 



