DEEP-SEA DEPOSITS 



99 



formation of plagioclase into orthoclase has occurred 

 through the substitution of sodium for potassium. An- 

 other find of MelHs and Norin of Uppsala concerns 

 layers of volcanic ash in cores from the eastern Medi- 

 terranean and the Tyrrhenian Sea.^ Thus, Mellis found 

 in cores taken southwest of Cyprus and south and 

 southeast of Crete layers of volcanic glass which had 



Fig. 35. Submarine weathering, plagioclase to ortho- 

 clase 



probably become deposited after the cataclysmic out- 

 break of the island volcano Santorin in the sixteenth 

 century b.c. Norin, in a core taken in the center of the 

 Tyrrhenian Sea, found a layer of ash which he was 

 able to identify with ash from old Mt. Somma, which 



