150 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



Chester series to run northeast. North of this point the rocks of the series 

 cease to be influenced by the granitic metamorphism which followed the 

 dynamic metamorphism in the rocks farther southeast, and consist entirely 

 of amphibolites, partly altered to serpentines, and treraolites changed to 

 steatite, while the inclosing feldspathic rocks change at the same place into 

 sericite-schists. 



(c) The enstatite of the black serpentine west of the limestone and 

 that in the limestone must have had the same origin. 



The two occurrences are identical in physical peculiarities, size, shape, 

 cleavage, luster, and tendency to serpentinization, and under the microscope 

 I find no difference in them. There is no more reason for giving them a 

 different explanation than in the case of the separate wernerite crystals in 

 the Bolton limestone and the massive wernerite rock which forms "the 

 border of the crystalline limestone on the granite, or the white pyroxenes 

 scattered in the Canaan limestone and the compact canaanite into which 

 it graduates, or the bladed tremolite regularly disseminated in the Lee 

 marble and the compact tremolite rock which is associated with it. 



In all these cases it is recognized that the bladed crystals have grown 

 in the limestone much as the bladed cyanites have grown in the quartzose 

 mica-schist adjacent to our serpentine, and that the only further assumption, 

 needed to explain the corresponding massive rocks is that the silicate has 

 in each case replaced all the carbonate, or that the solutions which brought 

 the silica into the limestone have removed the surplus of the carbonate. It 

 seems to me that the natural explanation here is that the massive enstatite 

 rock is simply the result of carrying the process which has formed the 

 enstatites in the dolomite a step farther to the almost complete replacement 

 of the latter; and, indeed, within what we have called the limestone, every 

 stage can be traced from pure limestone to a i-ock nine-tenths enstatite. 



(d) The enstatite not necessarily^ a proof of eruptive origin of the 

 rock. 



I know of no eruptive rock made up exclusively of coarse, long-bladed 

 enstatite, but I have .studied several beds of such character among the crys- 

 talline schists. 



I have collected the large, smooth-faced, altered enstatite crystals in 

 Norway, and they seemed to have formed as attached crystals, projecting 

 into free spaces in crystalline limestone, rather than as constituents of 



