14 PROCEEDINGS OF THE NATIONAL, MUSEUM. vol. G6. 



The composition of the Goose Creek rock is shown by the analysis 

 to be similar to that of the ordinary diabases and basalts of the 

 Newark series. The analysis gives the following norm, calculated 

 according to the quantitative classification. 



Norm of normal diabase. 

 Salic: Percent. 



Quartz 0. 18 



Orthoclase 6. 12 



Albite 17.82 



Anorthite 25. 02 



Total 49.14 



Femic : 



Diopside 18. 79 



H ypersthene 27. 62 



Magnetite 1. 39 



Ilmenite 2.89 



Apatite . 34 



Total 51. 03 



The rock falls in Class III, order 5, in the quantitative classifica- 

 tion and precisely on the boundary between rangs 3 and 4 so that 

 it can be placed either in subrang 4 of rang 3 (Camptonose) , or sub- 

 rang 3 of rang 4 (Auvergnose) . 



The norm does not differ greatly from the mode except in that the 

 hypersthene does not occur as such in the rock but enters into the 

 monoclinic pyroxene. There is less quartz than is to be expected 

 from the amount of orthoclase indicated, assuming that all of the 

 orthoclase occurs as micropegmatite. This is chiefly due to the dis- 

 crepancy introduced by calculating all of the alumina as anorthite 

 when, modally, it occurs in part in the augite as shown by the analysis 

 of the separated mineral. It was found instructive to go through the 

 procedure of calculating a "norm" for the analysis of the pure 

 pyroxene separated from the diabase which gave the following results : 



"Norm" of pyroxene analysis. 



Ilmenite 1. 52 



Anorthite 5. 84 



Diopside 55. 73 



Hypersthene 28. 75 



Fayalite 8. 98 



Total 100.82 



The interest and significance of this "norm" will be further dis- 

 cussed under the heading "differentiation." 



DIABASE PEGMATITE. 



The name diabase pegmatite is here applied to certain phases of 

 the rock which differ from the normal diabase chiefly in the size of 

 the constituent crystals. The name pegmatite is used in the looser 



