I. 



II. 



III. 



IV. 



V. 



Sp. gr. >2-69 



<2*69. 



>2'69 



<2-69 



<2'60 



Orthoclase 7*5 



7-7 



13-2 



12-6 



27-4 



Albite 47-1 



71-3 



60-6 



70-3 



68-9 



Anorthite 45'4 



2 1 •() 



26*2 



17-1 



3-7 



ab^aii! 



ab 7 ario 



ab 5 an 2 



ab 9 an 2 



abooari! 



J. Y. Leicis — Palisade Diabase of New Jersey. 161 



Composition of the Feldspars. — Feldspars were also separ- 

 ated and analyzed from the Rocky Hill material by Phillips and 

 from the West Rock locality by Hawes. Omitting non-feld- 

 spathic constituents and assigning the potash to orthoclase, and 

 the soda and lime to albite and anorthite, respectively, the 

 analyses show the following constitution : 



Mineral Constitution of the Feldspars. 



VI. ! VII. VIII. 



= 2-577>2'69 <2'69 



3] -7 6-0 7-2 



64-2 i 24-4 40-9 



4-1 ; 69*6 51'9 



ab 17 arii ab 3 an 8 ab 5 an 6 



I, II. Rocky Hill. Quarry near the middle of the trap sheet. 

 Ill, IV, V, VI. Rocky Hill, N. J. Old quarry near upper 

 contact. 



VII, VIII. New Haven, Conn. West Rock. 



The plagioclase molecules as calculated range from nearly 

 pure albite to labradorite. It is probable, however, that some 

 of the soda is combined with the potash in orthoclase and 

 anorthoclase. On the other hand, it is also quite possible that 

 small amounts of more basic plagioclases would have been 

 found if the heaviest portions had been further separated 

 before analysis. The frequent occurrence of zonal structure 

 in the plagioclases, however, seems to indicate that these 

 minerals do not occur in individualized grains of uniform 

 composition, but have been built up into composite crystals of 

 successively more acidic and more sodic character. In the 

 instances determined the portion with the highest specific 

 gravity constituted more than half the total feldspars, so that 

 the labradorite molecule undoubtedly predominates. 



Metamorphie effects. — Contact metamorphism has produced 

 an elaborate series of hornfels, rocks characterized by various 

 combinations of feldspar, biotite, quartz, augite, hornblende, 

 tremolite, garnet, spinel, magnetite, muscovite, cordierite, 

 scapolite, vesuvianite, sillimanite, andalusite, chlorite, calcite, 

 analcite, titanite, tourmaline, zircon, apatite, and possibly leu- 

 cite. The various types within the zone of metamorphism 

 seem to vary with the original composition of the shales, and 

 not to depend on relative distances from the contact nor degree 

 of metamorphism. 



Metamorphie arkose, both in the inclusions and at. the con- 

 tacts, contains besides the usual plagioclase, orthoclase, and 

 some quartz, also augite, biotite, epidote, cordierite, chlorite, 

 calcite, tourmaline, and apatite. 



