788 H. S. WASHINGTON DECCAN SALTS AND PLATEAU BASALTS 



by Harker, as typical of those of the subregion. The Skye flows were 

 subaerial and issued from fissures. They are of enormous volume in the 

 aggregate, the total thickness of the series of flows (and sills) being over 

 2,000 feet, the individual flows being from 20 to 50 feet thick. They 

 "show on the whole a remarkable uniformity of general character/' two 

 textural types being present, one porphyritic, with labradorite pheno- 

 crysts, and the other densely aphyric. The micro-texture is usually 

 ophitic, and they are composed, as are the other plateau basalts, of labra- 

 dorite and augite, with minor amounts of magnetite and apatite. Glass 

 seems to be comparatively rare. Exceptionally, olivine is present, rarely 

 as phenocrysts, and a few show phenocrysts of augite. The general chem- 

 ical characters are shown by the average given in Table IX, from analyses 

 given by Harker. The basalts appear to be, in general, not quite fresh, 

 which would explain the somewhat low silica and relatively high ferric 

 oxide. Harker (page 249) notes that Pollard determined quite notable 

 amounts of chromium and vanadium in a number of them, which is in 

 accord with the observations of Harwood and Holmes elsewhere. 



In Greenland there are two now distinct, but probably formerly con- 

 nected, areas of plateau basalts. The one is on the west coast and in- 

 cludes the basalts of Disco 24 and Hare 25 Islands. These form thick and 

 fairly extensive, horizontal flows, of ophitic texture and generally aphyric. 

 They have the usual composition of the plateau basalts, except that the 

 Disco basalts contain variable amounts of metallic iron, while the Hare 

 Island rocks seem to be free from this, but contain more or less olivine 

 as phenocrysts. An average of analyses of these West Greenland basalts 

 is given in Table IX. Little is known of the basalts of the two great 

 basaltic areas along the east coast of Greenland, but they would seem to 

 be much like the other Thulean basalts. 26 There is only one analysis of 

 them, but as the rock is not fresh, the analysis is not reproduced here. 



Of the rocks of Jan Mayen there is very scanty information. They 

 are predominantly basalts, but an segirite trachyte occurs, and the de- 

 scriptions of Scharizer 27 and Holmes 28 indicate that the rocks have 

 decidedly alkalic affinities. The basalts described do not greatly resemble 

 the usual Thulean or other plateau basalts, as the texture is not notably 

 ophitic, the plagioclase contains much -more of the albite molecule, 

 nephelite is present in some, and olivine seems to be common. The speci- 

 men analyzed by Harwood contained about 5 per cent of calcite, which 

 Holmes regards as primary. 



24 T. Nicolau : Meddel. Groenl., vol. 24, 1901, p. 215. 



25 Holmes and Harwood : Min. Mag., vol. 18, 1918, p. 182. 

 20 Holmes and Harwood : Op. cit., p. 189. 



27 R. Scharizer: Jahrb. geol. Keichsanst. Wien. vol. 34, 1S84, p. T(»7. 



28 Holmes and Harwood : Min. Mag., vol. 18, 1918, p. 202. 



