ART. 2. PETROLOGY AT GOOSE CEEEK— SHANNON. 85 



zeolites probably was not originally present in the solutions but was 

 derived from the plagioclase of the altered rock by substitution of 

 soda. The boric acid of the datolite and axinite, the sulphur of the 

 chalcopyrite and pyrite, and the fluorine entering the apophyllite 

 near the end of the series were doubtless from the magma. 



It appears then that the solutions were rich in soda in some form 

 possibly combmed with siHca in solution, and contained appreciable 

 amounts of boric acid, sulphur, and fluorine. Bailey and Grabham^« 

 have considered that the solutions forming the end product of cooling 

 of a basaltic magma are richly charged with sodium carbonate in 

 solution. Such a solution might be capable of producmg all of the 

 effects here described, although one objection to assuming the soda 

 in the solutions at the Goose Creek localitv to have been in the form 

 of carbonate is the very limited amount of calcite there found. 



EXPLANATION OF PLATES. 



Plate 1. 



^^^Diabase pegmatite intrusive as a tabular body in ordinary diabase. ^ natural 



Plate 2. 



Upper: Aplite dike in contact with normal diabase. The aplite is cut by later 

 cracks of two ages, the first filled with diopside and the second (along which the 

 specimen is broken) filled with laumontite. ^ natural size 



. -^i?!^'^',', ^^"""^ ^^P^cimen of diabase pegmatite showing long blades of augite 

 with diallagic parting, etc. ^ natural size. 



Plate 3. 



Diabase pegmatite in ordinary diabase, cut by later seam along which hvdro- 

 thermal alteration has changed the augite to hornblende, etc. ^ natural size 



Plate 4. 



Upper: Photomicrograph of ordinary diabase showing structure, outlines and 

 Is'diaTet^'ers^"^'*' ^"""^ ''''^"^''' ^""'"^ ""^ ''°'' '''^- ^^^^^^^^ ^'^ht. Magnified 



Lower: Diabase pegmatite showing large augites, feldspars partly replaced by 

 sencite, and interstitial micropegmatite. Ordinary light. Magnified 13 diameters. 



Plate 5. 



Upper: Diabase pegmatite cut by a seam along which hydrothermal deposition 

 ^hornblende has taken place. The black portion of the field is hornblende 

 with some clilorite. The gray is altered feldspar and the white is quartz. The 

 section shows the replacement of altered feldspar of micropegmatite bv horn- 

 blende giving quartz-hornblende micrographic intergrowths. To the right at the 

 bottom of the picture is an area of hornblende which still contains a core of unre- 

 placed augite. Ordinary light. Magnified 13 diameters. 



6/pp':'2?olt'im' """ '^- ^"'''"- ^'^'"-"- °f basic Plagioclase feldspars. Geol. Magazine, vol. 



