338 GEOLOGY OF OLD HAMPSHIEE COUNTY, MASS. 



In otlier crv.stals this change has proceeded in every degree until the 

 crystal becomes wholly changed to a fibrous hornblende (uralite), in which 

 the black inclusions of the diallage still remain, and indeed appear often to 

 be considerably increased at the expense, it would seem, either of the red 

 inclusions or of the diallage itself, and to possess in the hornblende a very 

 distinct zonal arrangement. Furthermore, the hornblende itself is in most 

 cases changed more or less into an aggregate of rounded green scales of 

 chlorite, but slightly diclu-oic, which has in many cases eaten into the 

 center of the hornblende in great patches, in others has surrounded it in 

 a regular layer. 



Finally, very peculiar and delicate plumose aggregations of elongate, 

 round-ended scales of biotite are gathered in tufts at spots along the outside 

 of the chlorite and attached to it, or a group of such tufts radiates from a 

 center in which, in each case, remains of the green chlorite scales appear. 

 The whole an-angement suggests very strongly the derivation of the biotite 

 from the chloritic mineral parallel with the decomposition of the feldspar. 

 In another case a flat patch of the green chlorite scales seems to change 

 gradually into a mass of brown biotite scales, some of the small plates 

 having the green color and weak pleochroism of chlorite at one end and the 

 brown color and strong pleochroism of biotite at the other, and these latter 

 pass into a single large biotite crystal, so that one can hardly avoid con- 

 cluding that the biotite has been derived, in part at least, from the diallage 

 through the hornblende and chlorite stages. The earliest stage may, of 

 course, have been with diallage surrounded by biotite, and the change to 

 chlorite may have proceeded Ijoth ways from the boundary. 



Many slides cut from various parts of the area show no remains of the 

 diallage, but only the fibrous hornblende containing the zonally arranged 

 black inclusions, and having chlorite and biotite ai-rauged with regard to it 

 exactly as in the slides where the diallage is present. We may thus con- 

 clude that the diallage was once widely and abundantly present in the rock. 



Apatite occurs in exceptionally large crystals in the hornblende. 



To the above description of the pyroxenic varieties are added some 

 special notes upon the commoner and more altered biotite amphibole granite, 

 or tonalite, and upon one or two rare varieties. 



The quartz is everywhere distinctly subordinate to the feldspar, and 

 molds the latter. At Elizabeth Rock, in the north of Northampton, it is 



