THE CHESTER AMPHIBOLITE AND SERPENTINES. 97 



caiTving orthoclase. With the microscope liomblende in broad plates witli 

 strongest pleochroism and al^sorption; c>b>a, c--deep bhie, b-deep 

 olive, a=straw yellow. Extinction 17° 30'. 



Orthoclase is abundant ; plag-ioclase occurs with extinction 24"^. Little 

 magnetite and no leucoxene. Epidote is abundant. 



3. A m2)hibolit('.— Chester; cutting near railroad station on the west. 

 (See PI. VI, fig. 4, and p. 160.) A finely banded rock; interrupted sheets 

 of white feldspar grains rather distantly placed in ground of jet-black 

 hornblende needles of high luster, all parallel to the common direction of 

 the stretching. 



Under the microscope, stout, long blades of very deep-green horn- 

 blende, with distant basal partings and almost no prismatic cleavage visible, 

 show the strongest pleochroism and absorption I have ever seen, the 

 formula for which is the same as in the last case. Between the bands of 

 these stout blades a coarse, limpid mosaic of plagioclase grains occurs, and 

 very little magnetite appears in the slide. The plagioclase is an oligoclase 

 with positive bisectrix and extinction at +9° to the trace of the basal 

 cleavage on M [010]. 



THE SERPENTINES AND ASSOCIATED MAGNESIAN ROCKS. 



In the long hornblende-serpentine band which stretches across the 

 State from Rowe to Granville, looping back in the last town so as to be 

 repeated three times in an east-west line, the serpentines and associated 

 rocks present a great variety, both as to present status and as to origin, and 

 one can distinguish hornblende-serpentines, pyroxene-serpentines, enstatite- 

 serpeutines, and olivine-serpentines. 



There are associated with these serpentines beds of clinochlore, tremo- 

 lite, actinolite, corundum, magnetite, steatite, talc, and, in smaller quantity, 

 deweylite, dolomite, magnesite, clu-omite, chalcedony, picrosmine, diaclasite, 

 bastite, and "phsestine." 



Of these the first five represent in general the results of other lines of 

 change than that which has ended in serpentine, or at times a stage antece- 

 dent to the change into the latter mineral. 



The talc and steatite can be traced back to tremolite or actinolite with 

 or without the intervention of a serpentine stage, or, the purer talc especially, 

 to serpentine of any origin; the secondary dolomite, magnesite, magnetite, 



MON XXIX 7 



