542 THE DISTRIBUTION, ETC., OF ALKALINE ROCKS, 



In Sumatra alkaline trachytes and phonolites have been noted 

 but no details are known. Very ancient crystalline rocks (schists, 

 etc.) are known in this island, and the lavas have burst through 

 them and the overlying Carboniferous and Eocene sediments.* 

 The volcanic rocks range from Miocene to Recent. 



The Island of Socotra has microgranitic intrusives bearing 

 riebeckite, probably of Tertiary age, and is, according to Suess, 

 probably a fragment of the Abyssinian massive separated from it 

 by the subsidence of the Gulf of Aden. The alkaline rocks have 

 intruded the Archaean fundamental complex, and probably also 

 the overlying Cretaceous sandstone. 



From Celebes a number of leucite basalts, leucitophyres, leuci- 

 tites, and melilite nepheline basalts have been recorded by A. 

 Winchmann.f Here too the lavas are early or middle Tertiary, 

 and lie close to ancient schistose rocks and border on gigantic 

 earth-fractures. 



Both Sumatra and Celebes are looked upon as horsts or relics 

 of ancient continents, Sumatra being like Socotra, a remnant of 

 Lemuria (the Indo- African continent), and Celebes a remnant of 

 the Sino- Australian continent of Neumayr. In these positions 

 then we have the alkaline lavas as in Bohemia, Central France, 

 etc., superimposed on horsts. 



In those ranges of the Tien-Chan group which are directed 

 north-west, occur diabases, melaphyres, dolerites, teschenites, and 

 porphyrites; in those directed north-east, granites, granitites, 

 porphyroids, syenites, orthophyres, gabbros, etc.; in those directed 

 east and west, gneiss and ancient crystalline rocks. J Therefore 

 in this great mountain-group both plutonic and volcanic alkaline 

 rocks occur. I have unfortunately not been able to peruse any 

 of the papers in which their occurrence is described. However, 

 here again the situation is closely analogous to occurrences else- 

 where. The Tien-Chan Mountains are situated to the north of 



* Verbeek, Top. en geol. Beschr. v. Sum. Westkust, 1883. 

 f Naturkund. Tijdschr. Ned, Ind. Part iii. p. 3 15, quoted from Min. Mag. 

 Vol. xi. 



X Suess, ' La Face de la Terre,' Vol. i. pp. 616-620. 



