544 THE DISTRIBUTION, ETC., OF ALKALINE ROCKS, 



centres of such basins, and are never met with in great folded 

 ranges composed mainly of these sediments like the Alps and 

 Himalayas. 



(3) Alkaline rocks may occur in folded ranges on the flanks of 

 horsts where folding is mainly superficial and fracturing plays 

 the more important part as in the Tien-Chan Mountains, the 

 Carpathians, Transylvania, and the Banat region, and possibly 

 South-west Portugal is also such an area. 



(4) The monzonites and adamellites of Tyrol which occur in the 

 Alpine regions are not truly alkaline, though they furnish a link 

 between the calcic and alkaline series. The modern lavas of 

 Vesuvius, Etna and Stromboli have similarly alkaline affinities. 

 Both these areas, and many others in which similar rocks are 

 found, occupy anomalous positions. The Tyrrhenian area is a 

 subsided portion of the Pelitoranian massive, and constitutes the 

 subsided Ruckland of Apennine folding, yet it is now an area of 

 heavy sedimentation, and changes are probably going on whereby 

 this area is becoming the centre of a basin, or perhaps a Vorland. 

 Such rapid readjustments naturally produce confused conditions 

 whereby the lavas erupted have affinities both with continental 

 and oceanic volcanic rocks, and are in fact alternately alkaline 

 and calcic, or a mixture of both. The Tyrol area formed a 

 portion of the subsided Ruckland at the time of the commence- 

 ment of the Alpine folding, being situated close to the western 

 border of the Servo-Croatian massive, but it is at the same time 

 a portion of the Adriatic subsidence-area, the subsided Vorland 

 of the Apennine fold (Suess). 



Complexities of this kind are frequent in Eurasia, but are not 

 common in continents like South America, Africa, and Australia, 

 which form homogeneous masses. 



(5) The alkaline lavas of many of the Ionian and JEge&n 

 Islands* rise along the fractures which produced, in the Tertiary 

 epoch, the basins of the Eastern Mediterranean and ^gean. 

 These basins constitute subsided fragments of a plateau (Suess). 



* ' Petrograph. Sketch of jEgina and Methana,' by H. S. Washington, 

 Journ. of Geol. Vol.ii. No. 8. 



