F. A. P err et— Vesuvius. 



Fig. 13. b 



429 





1 



1 



p 





■> . > 



ii V 



4. 



4 



\, 



Fig. 13. Vesuvius — Four phases of a small internal avalanche. 



Am. Jour. Sci.— Fourth Series, Vol. XXVIII, No. 167.— November, 1909. 

 29 



