THE CHESTER AMPHIBOLITE AND SERPENTINES. 115 



of highly retractive epidote, which have passed unchanged from the parent 

 rock, and often show traces of its stratification. It wouhl seem, then, to have 

 been derived from the common epidotic hornblende-schist (amphibolite) 

 with which it is associated. In a great number of slides no trace of olivine 

 or enstatite, or of the structures characteristic of these minerals, could be 

 detected except in the bowlders from Chester (Massachusetts Survey Col- 

 lection, XIII, No. 53), whose exact locality can not be determined, and 

 those from the base of the large Middlefield bed, from which place the 

 Chester bowlder may have come. The presence of so large masses of 

 chi-omite and of nickel requires explanation, and indicates that some parts 

 of these beds were once chrysohtic. The specimen labeled XIII, No. 43, of 

 the Massachusetts Sui-\'ey Collection, from Chester, probably from the south 

 end of the large Middlefield bed, where is an old " mine " of this ore, is a 

 mass of chromite 50""" on a side. Moreover, the discovery that the so-called 

 quai-tz pseudomorphs from the Middlefield bed are serpentine pseudomorphs 

 after olivine^ must receive consideration in this connection. They are, how- 

 ever, large, perfectly terminated crystals, some of which have broken off from 

 the walls of the Gavitj to which they were attached, and they can not be 

 taken as normal idiomorphic constituents of an ultra basic eraptive. They 

 are better explained as fissure minerals hi a crystalline limestone, like the 

 Snarum crystals. 



I conclude, therefore, that nearly all of these serpentines are derived 

 from the amphibolites, and find the stratigi-aphical e%adence in this direction 

 strengthened by the lithological e\ddeuce. 



Osbom's quany at Blandford is a dividing point between the trans- 

 lucent hornblende-serpentmes on the north and the black enstatite-seiiien- 

 tines on the south. To the east of the central steatite bed, which is 

 quan-ied, is the isolated and unique oli vine-serpentine bed; to the west is 

 the equally peculiar sahlite-serpentine bed. 



The black serpentine and dolomite mass which forms the center and least 

 changed portion of the central steatite bed is the first of a series of such 

 deposits wliich locally replace the amphibolite in its further progress south. 

 They are rare and subordinate to amphibolite in the broadened portion of 

 the lied across West Granville, but after the bed has bent northward at 

 East Granville they increase in relative importance and are associated with 



1 See BuU. U. S. Geol. Survey No. 126, 1895, p. 91. 



