12 



HENRY S. WASHINGTON 







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dikes and flows of basalt penetrate the 

 tuffs. But it seems to be equally clear 

 that, while the period of formation of 

 the tuff cones antedated that of the lava 

 ones, yet that in some cases, at least, the 

 closing phases of the tuff cones coincided 

 with the activity of the lava and cinder 

 ones, as is shown by the intercalation 

 of tuffs and lavas on the southeast slope 

 of Monte Vulcano, and the intermingling 

 of the tuffs of Monte Pozzolana and the 

 scoriae of Monte Ponente in the upper 

 portions of the mass. The usual pres- 

 ence of blocks of lava, scattered through 

 the tuffs, points to the existence of lava 

 flows beneath the surface at the time of 

 the tuff eruptions, fragments of which 

 were hurled up with the looser material. 

 It might seem that the blocks in the tuff 

 of Monte Levante have been ejected from 

 the neighboring Monte Vulcano, as they 

 are especially prominent in the upper 

 beds. But this supposition is negatived 

 by the fact that, while chemically similar 

 to the later lavas of Vulcano, they belong 

 to a different petrographic type, similar 

 to that of the blocks in the other tuffs, 

 and quite distinct from the usual types of 

 the later lavas, as will be brought out 

 later. 



As to the geological age of these 

 eruptions, the total absence of sedimen- 

 tary and fossiHferous rocks precludes any 

 definite evidence. But the well-preserved 

 state of the cinder cones, the sharpness 

 of outline of their craters and of the 

 barranca at Monte Rosso, and the gen- 



