THE CHESTER AMPHIBOLITE AND SERPENTINES. 151 



eruptive rock. Also the eustatite rock, as 1 have seen it at tlie Till}' Foster 

 mine, is a member of a highly metamorjjhosed crystalline-schist series. It 

 resembles quite closely what the Westfield rock ma\- ha\e been, but is finer- 

 grainerl. 



It is to be further remai-ked that tlic massive structure of the l)liick 

 serjjentine is not a characteristic indicating, necessarih', an eruptive origin, 

 since the rock is made up of elongated square prisms, often 3 to S 

 inches long, interlaced, and witli calcite in the interspaces. It is like the 

 massiveness of the Bolton rock, or the canaanite. The black color also is 

 wholly the product of sei'pentinization, as the freshest enstatite is ever^'- 

 where translucent and pale-gray. 



(e) I therefore conclude that the rock was once a bed considerably 

 thicker than the present one, and consisted of a somewhat ferruginous dol- 

 omite, which was permeated by heated siliceous solutions, set in motion hv 

 the large granite batholites, upon their intrusion into their present positions. 



The ferruginous enstatite (the serpentine derived from it contains H to 

 9 per cent of iron) was formed bv the reaction of these solutions with the 

 magnesium of the carbonate, and the resulting carbonated waters may have 

 promoted the solution and removal of a part of the unaltered calcium car- 

 bonate, and this may have been the condition necessary to the formation of 

 the pure enstatite rock of the west wall, which differs only in the almost 

 complete absence of the calcite. The analogy of the werneritedimestone, 

 the canaanite-limestone, and the tremolite-limestone, and of the correspond- 

 ing massive silicate, nearlv free from carbonate, seems to me complete for 

 the explanation of the enstatite-limestone, and of the massive enstatite of the 

 western border of the Westfield quarry and the similar beds farther north. 

 Indeed, the change of the limestone at tliis locality into tremolite, for a 

 certain distance in, along the eastern Ijorder, and the partial change into 

 tremolite throughout, seems not essentiallj- different from the earlier 

 change, for a greater distance inward, into enstatite. 



The idea that the black serpentine at the Westfield quarry is an altered 

 dike rock, and that the marble only is an altered sedimentary limestone, I 

 can not entertain for a moment. The identity of the black prisms in the 

 limestone with the black prisms wdiich are interlaced to form the massive 

 rock seems to me fatal to this theory, especially Avhen we consider those 

 parts of the limestone which are nearly all composed of tlie black rods. 



