30 NEW YORK STATE MUSEUM 



no. 5 is a hornblende gabbro; no. 8 is a gabbro-diorite ; nos. lo, 13, 

 and 14 are hornblende syenites; no. 11 is a monzonite ; and no. 12 

 is a diorite. The large number of minerals — sixteen in all — is also 

 notable. It is also important to note that in the above table, nos. 3 

 and 4, 7 and 8, 9 and 10, and 11 and 12, respectively, come from 

 single stocks. 



The predominating mineral is feldspar which ranges from labra- 

 dorite alone in some rocks through all stages, to those rocks which 

 are rich in the more acid plagioclases or orthoclase. 



Hornblende, generally in considerable amount, occurs in all but 

 one (no. i) of the rocks. Sometimes it makes up a fourth or more 

 of the whole rock. Much of the hornblende in the more basic rocks, 

 at least, is of secondary origin and forms corrosion rims (below 

 described) around other minerals. Its color varies from green to 

 brown. In one slide many examples of the transition from pyroxene 

 to hornblende are perfectly shown. 



Hypersthene, with a single exception (no. 5), is an important 

 cpnstituent of all the more basic types. It is almost always highly 

 granulated and with pleochroism from greenish gray to pale reddish 

 brown. 



Augite and diallage of greenish gray color and with good cleavage, 

 are only occasionally present and rarely as important constituents. 



Ilmenite is invariably present in amounts up to 5 per cent and 

 often with transition to leucoxene. 



Pyrite in small amount seldom fails. 



Biotite and garnet of the usual sort, though mostly in tiny flakes 

 or grains, are present in moderate quantity in all but certain of the 

 more acidic facies. The unusually high percentage of garnet in no. 4 

 is a fine-grained border phase of a stock. 



Quartz, in small irregular shaped grains, is wholly confined to the 

 acidic types. 



Zoisite, in small stout prisms, sometimes makes up about i per cent 

 of the rock. 



Zircon and apatite, in very small quantities, are almost wholly 

 confined to the acidic facies. The usual absence of the apatite from 

 the typical gabbros is especially noteworthy. 



Olivine was noted in but one case (no. i) and this in the only 

 rock from which hornblende is missing. 



Titanite in a few small grains was noted in no. 11, 



Reaction or corrosion rims. Reaction or corrosion rims, which 

 are well known in many basic rocks, are exhibited in a truly re- 



1 



