ART. 



PETROLOGY AT GOOSE CREEK SHANNON. 29 



The norm calculated from the analysis of the Goose Creek aplitic 

 dike, column 1 above, is as follows: 



Norm of Goose Creek Triassic aplite. 

 Salic : 



Quartz 25.98 



Orthoclase 3. 89 



Albite 49. 78 



Anorthite 7. 51 



Apatite Trace 



Total 87. 16 



Femic: 



Magnetite 1- 39 



Titanite .78 



Hematite • 32 



Diopside 7. 99 



Hypersthene 1- 60 



Total 12. 08 



This analysis, according to the quantitative classification, falls into 

 class I, order 2, rang 2, subrang 5. The similarity of the composition 

 of thf^ rock to that of the albitic pegmatite is marked. It is obvious 

 that the aplites are, like the albitic pegmatites, final products of 

 a process of magmatic differentiation which yielded small amounts 

 of a fluid acid residuum rich in water, this having been, in the case 

 of the aplites, squeezed up narrow cracks in the solidified diabase. 

 These rocks, as represented by the above analysis, are much more 

 acid than any differentiate of the Triassic diabase yet described; 

 this is shown by comparison with the two analyses quoted, which 

 represent the most acid rocks previously known from the Newark 

 series. These are likewise albitic rocks but lack the abundant 

 quartz of the Goose Creek aplite. 



So far as the magmatic processes are concerned in the production 

 of the rock types here considered there are but three phases, first the 

 normal diabase, second the diabase pegmatite, and third the albitic 

 rocks. The normal diabase grades into the diabase pegmatite by 

 gradual coarsening of grain but there seems to be a sharp break in 

 composition between the diabase pegmatite and the highh' acid al- 

 bite rocks. The fourth product of the magmatic differentiation which 

 need be mentioned here is probably water, charged with materials in 

 solution, which doubtless produced all of the hydrothermal changes 

 hereinafter considered. 



Differentiation of this sort is not well exposed at many places in 

 the Newark series and no example as extreme and striking as that 

 at Goose Creek has heretofore been described in the rocks of this 

 system. J. Volney Lewis, in considering the Palisade sill, has shown 

 that the main mass of the rock is a somewhat quartzose diabase which 

 has probably originated by gravitative differentiation through the 



