ELIZABETHTOWN AND PORT HENRY QUADRANGLES 43 



former which is more abundant. There may be a little H2O in 

 the biotite, but it has all been assigned to kaolin. The division of 

 the CaO among anorthite, pyroxene, garnet and possible hornblende 

 is purely an estimate. In the recasting about two thirds the mole- 

 cules were assigned to the anorthite, while the remainder were 

 allotted to garnet and pyroxene (including hornblende). The FeO 

 and MgO had to be divided between biotite (a relatively small por- 

 tion) and pyroxene (hornblende). Some FeO was also used for 

 garnet. There is more than enough AI2O3 for the feldspar, biotite 

 and garnet, so that a small residue was placed in the pyroxene as is 

 doubtess justifiable. All the FeaOg was used for magnetite, as this 

 assumption did not yield any more than is obviously present in the 

 slides. The composition of the garnet was necessarily assumed to 

 involve both the grossularite and the almandite molecules. There 

 is probably a little TiOg in the rock but if so it is presumably in the 

 magnetite for no titanite worth mention was observed. After all 

 these assumptions, suggested or checked by estimates of the relative 

 abundance of the minerals as seen under the microscope, the above 

 result was reached. It is difficult to believe that a molten. magma 

 of only 50.54 per cent silica would crystallize directly from fusion 

 so as to yield this excess of silica forming 3.60 of quartz. If we 

 recast without using the garnet molecule and with the allotment as 

 usual of all the alumina remaining above the orthoclase, albite and 

 kaolin, to the anorthite, only a tenth as much or about .30 remain 

 uncombined. The natural inference follows that the garnet has 

 resulted from metamorphic reactions between the pyroxene and 

 anorthite, in which the lime and alumina of the latter were utilized 

 and the silica left free. 



The Woolen Mill locality is not the only one for this variety of 

 rock, or at least for one that to the eye appears to be the same. 

 Blueberry mountain along the southern border shows the same 

 general aspect with occasional large blue crystals of labradorite. 



New Pond locality of a peculiar gabbro. Along the road lead- 

 ing into New pond and an eighth of a mile before it terminated 

 at the pond itself, a ledge of a very pecuHar eruptive was found, 

 which differs from all others mentioned. It consists of sharply 

 angular crystals of plagioclase, rectangular in cross section, im- 

 bedded in a dark green matrix of what proves under the microscope 

 to be granules of augite. This rock has been seen in boulders 

 within a mile or so of the locality mentioned and may be more 

 widely distributed. It has also been seen in the Mt Marcy quad- 

 rangle along the highway about a half mile south of Beede's. The 



