28 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 66. 



The example of these aplites which was selected for analysis was a 

 dike about 2 cm. in width which penetrated fresh and unaltered dia- 

 base. Under a lens this shows abundant albite and quartz with con- 

 siderable pale green diopside and a few scattered crystals of titanite. 

 It also contains a few grains of diopside full of inclusions surrounding 

 nuclei consisting of short portions of blades of titaniferous diallagic 

 augite, apparently fragments broken from the wall of the crack where 

 it intersected a pegmatite mass, and arrested in process of alteration 

 by the aplite magma. Under the microscope this rock shows a border 

 made up of beautiful quartz-albite micropegmatite grown outward 

 from the wall along with an occasional colorless prismatic crystal of 

 diopside. The micropegmatite is well shown in the photomicrograph, 

 plate 9, upper. The central portion of the narrow dike consists of a 

 granular aggregate of albite with less quartz and some clear colorless 

 diopside. All of the albite is muddy. The results obtained upon 

 anal^^sis of this rock are given in column 1 of the following table. In 

 column 2 is given the analysis by Hillebrand of the holyokeite or 

 'Svhite trap" described by Emerson as fragments associated in an 

 agglomerate above the main extrusive Triassic diabase of the Connect- 

 icut Valley in Massachusetts^ and in column 3 is repeated the analysis 

 by Washington of the thin acid dike described by Hovey ^° as kerato- 

 phyre from Fair Haven. Connecticut. 



Analysis of diabase aplite and related rocks. 



•Benjamin K. Emerson. Holyokeite, a purely feldspathic diabase from the Trias of Massachusetts. 

 Journ. Geol., vol.10, pp. 508-512, 1902. 

 '"E.G. Hovey. Amer. Journ, Sci., vol. 3,1897, p. 237. 



