200 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



basal sections, it is observed that prism faces are poorly developed as 

 compared with the pinacoids. There are traces of a rude and 

 irregular parting parallel to these latter surfaces. 



In spots it is partially altered with the separation of yellow and 

 black iron oxides, the former hydrous. Along the cracks chlorite 

 is slightly developed. Twinning with the twinning plane (100) 

 was observed in several instances. The pyroxene is closely related 

 to the augite group. With the feldspar it is often enclosed in the 

 metallic portions. 



The feldspar of the basalt is in two generations. The crystals of 

 the first separation often attain a length of 3 mm., the microlites 

 often sinking to ultra-microscopic dimensions. At times the larger 

 feldspars exhibit undulatory extinction ; they were undoubtedly sub- 

 jected to strain during the closing stages of magmatic consolidation. 

 The feldspar is in a perfect state of preservation, colored occasionally 

 by the presence of hydrous iron oxide, especially in the immediate 

 region of the iron inclusions. Its high symmetrical extinction lying 

 between 35° and 40° indicates a feldspar of the composition Ab^An^. 

 It is, therefore, a feldspar of the labradorite-bytownite group. 



Magnetite (and this is the only remaining constituent noted in any 

 considerable amount) is relatively abundant. It occurs in irregular 

 elongated forms, often approaching a dendritic development, but 

 the typical skeleton-like development was not seen. It is especially 

 abundant in the region of the native iron, and here a rude fluxion 

 structure of the entire basaltic portion of the rock was noted.^ 



The remaining basalts, collected from the vicinity of Kaersut, are 

 of the usual olivine and non-olivine varieties, much decomposed and 

 presenting nothing of unusual interest. Their detailed description 

 will, therefore, be omitted. 



Lying loose, just back of Kaersut, occurs a peculiar rock (Cat. 

 No. 75,488) which deserves more than passing notice. It is brown- 

 ish-red in color on the fresh fracture and is traversed by tiny veinlets 

 of calcite ; this latter mineral, however, is not confined to particular 

 strips, the rock effervescing in all parts on the application of acid. 

 Although of a coarsely crystalline character, with the exception of 

 an occasional rather large irregular patch of tarnished olivine, the 

 character of the ground mass cannot be made out with ease. The 

 olivines, for the greater part, glisten in reflected light, and present a 



^ For a very complete bibliography on the iron-bearing basalt of Greenland, 



see Dr. Th. Nicolau, Meddelelser om Gronland, xxiv, 1901, p. 217, and for a 

 brief resume on the work done on the nickeliferous iron in the basalt of 

 Greenland, see Gisement et Nature du fer nickelifere du Gronland, by F. 

 Johnstrup, published in Meddelelser om Gronland, iv, pt. 11, 1893, p. 270. 



