LINOSA AND ITS ROCKS 33 



characterized by father low sihca and alumina, high iron oxides, with 

 ferrous oxide largely predominating over ferric, rather high magnesia 

 and lime, the former being very high in the olivine-rich type, rather 

 high soda (for such femic rocks), and low potash, very high titanium 

 dioxide, small amounts of phosphoric pentoxide and manganese, and 

 finally the constant presence of nickel oxide in rather high amounts 

 for this constituent. Zirconium, chromium, copper, barium, and 

 strontium seem to be either uniformly absent or present only in 

 traces. 



As regards the succession, or order of eruption, of the lavas, their 

 uniform and monotonous character in general gives little scope for 

 distinctions. From the figures furnished by the analyses of the tuffs 

 and the blocks of the cones of the earlier period, however, as compared 

 with those of the later lavas, it would seem that the earlier rocks were 

 slightly higher in soda, and in general somewhat lower in silica and 

 possibly in lime, than the later ones. The iron oxides, potash, tita- 

 nium, and phosphorus apparently change but little, while there are 

 indications of a slight drop in magnesia, though the high figure for 

 this constituent in the Monte Raneri lava (which, however, is earlier 

 than those of Monte Ponente) is anomalous. But the figures show, 

 in general, variations of too slight an extent to justify any definite 

 conclusion that a decided change has taken place, and indicate, on 

 the contrary, that the chemical character of the magma has remained 

 practically the same from the earliest eruption on Linosa to the latest. 

 It is possible that this is connected with a short period of volcanic 

 activity on the island, or it is possibly indicative of this. In the 

 absence of any geological or stratigraphical means of measuring the 

 time elapsed since the first eruptions, the interval between those of 

 the tuff and of the lava cones, and the time that has passed since the 

 last volcano became extinguished, we are not in a position to decide. 



Relations of the Linosa lavas to others. — In a paper ^ published 

 some years ago a possible genetic connection was suggested between 

 the lavas of Linosa, Pantelleria, and Sardinia, the suggestion being 

 based on the few analyses of the rocks of Pantelleria and Sardinia 

 which had been pubhshed at that time, none of Linosa being known, 

 as well as on some more general tectonic grounds. In a more recent 



I H. S. Washington, American Journal of Science, Vol. VIII, 1899, p. 293. 



