86 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.66. 



Lower: Diabase pegmatite — somewhat altered. The most conspicuous feature 

 of the field is the large skeletal growth of iron ore largely confined to an altered 

 pyroxene crystal. The interstices of the iron ore are filled with secondary 

 biotite and the feldspar of the micropegmatite at the bottom of the plate is 

 largely replaced by biotite and hornblende. Ordinary light. Magnified 13 

 diameters. 



Plate 6. 



Albitic pegmatite in normal diabase, showing feathery albite-diopside micro- 

 graphic intergrowths. i% natural size. 



Plate 7. 



Upper: Photomicrograph of the analyzed albitic pegmatite. The plate shows 

 the characteristic composition and structure of the rock. The large gray pris- 

 matic grains and the gray material of the micropegmatite is albite. A spear- 

 shaped prism pointing downward from the top of the photograph to the left of 

 the center is diopside and this connects with an intergrowth of diopside and 

 albite. Ordinary light. Magnified 13 diameters. 



Lower: An albitic pegmatite devoid of quartz and micropegmatite. The clear 

 mineral is colorless diopside and the gray is kaolinized albite. The large irreg- 

 ular dark areas in the section are skeleton magnetites largely replaced by titan- 

 ite and filled with chlorite. Ordinary Hght. Magnified 13 diameters. 



Plate 8. 



Albitic pegmatite grading into diabase pegmatite. Shows long blades of dial- 

 lagic augite. At the lower end of the specimen the groundmass is largely pla- 

 gioclase but the feldspar of the balance is albite. The long pyroxene blades are 

 replaced along their borders and at the tips by diopside. -y^ natural size. 



Plate 9. 



Upper: Micropegmatite in patches growing out from the wall (left) toward 

 the granular center of the analyzed aplite dike. Ordinary light. Magnified 13 

 diameters. 



Lower: Albitic pegmatite from waU of the mass illustrated in Plate 6. Ordi- 

 nary light. Magnified 13 diameters. 



o 



