702 H. S. WASHINGTON DECCAN SALTS AND PLATEAU BASALTS 



hind doubtful!} 7 — that they are parts of the same province. Holmes also 

 includes basalts from Kuszkin Island, at the mouth of the Yenisei, with 

 his Brito- Arctic basalts. On the whole, however, in view of the paucity 

 of our knowledge of them, the vastness of the area covered by these flows 

 and their eastward extension, the peculiar tectonic features as described 

 by Suess and Backlund, and the intervention of ISTova Zembla and the 

 Samoyed Urals (virgate extensions of the Ural Mountains), it seems 

 best to consider this Siberian basaltic area as distinct from the Thulean. 

 According to Suess : 



"These mighty Siberian flows have in all likelihood a common origin. In 

 some places at least their extrusion has persisted up to very recent times, but 

 the date of their first appearance is unknown. Nowhere is a volcano of any 

 importance to be seen. The presence of small ash cones tends rather to eon- 

 firm than to refute the view put forward in recent times, that these great 

 flows do not take place from isolated throats, but from a network of fissures." 



So little is known of these basalts petrographically that a few words 

 must suffice for their description. According to Chrustschofr 34 and Ahl- 

 burg, 35 the basalts of the main central areas are of fairly uniform char- 

 acter. They are rather coarse grained, composed largely of labradorite 

 and enstatite-augite, sometimes with and sometimes without olivine, and 

 some of them with much glass. The noncrystalline forms are ophitic. 

 The basalts from the eastern part of Siberia, according to Backlund's 

 descriptions and analyses by Sahlbom, are decidedly more alkalic, some 

 of them being called trachydolerite and others nephelinite. Backlund 

 notes the very late period of crystallization of the magnetite. The 

 analyses of true basalts from this vast region are so few or so imperfect 

 that it seems to be scarcely worth while to quote them here. So far as 

 they go, they indicate general chemical characters in harmony with those 

 of the better known plateau basalts, although the iron oxides do not seem 

 to be quite as high. 



In connection with the Siberian and the previously described Thulean 

 basalts, it is worth noting that von Wolff 36 considers that these and other 

 such vast areas of basaltic lavas can not be referred to either the Atlantic 

 or the Pacific clans of Harker and Becke. He proposes the recognition 

 of a clan, of equal rank with the other two, which he calls the "Arctic'' 

 and whose chief chemical characters are those of these plateau basalts and 

 their differentiation products. He suggests that the charnockite-anor- 



34 K. von Chrustschoff : Bull. Acad. Imp. Sci. St. Petersburg (2). vol. 34, 1S92, pp. 

 193-224. 



35 J. Ahlburs: Zeits. prakt. Geol., vol. 21, 1913, p. 108. 



36 F. von Wolff : Der Vulkanismus. vol. i, 1914, p. 153. 



