Vol. 6$^] BASALTS OF THE WESTERN MEDITERRANEAN. 73 



be remarked, however, that the low summations of some of the 

 analyses are undoubtedly due to these non-determinations, especially 

 of nickel-monoxide and manganous oxide. 



Of these analyses, the first four are representative of the Cata- 

 lonian basalts, No. 1 of the volcanoes near Gerona, 2 of the more 

 felspathic camptonose (felspar-basalt) - flows, 3 of the abundant 

 limburgose (nephelite-basalt)-flows, which filled the valleys near 

 Olot, and 4 of the scoriaceous lavas of the numerous small, recent 

 cones. The next four include representative Sardinian basalts : 

 No. 5 of some of the extensive Tertiary sheets, 6 & 7 of the basaltic 

 mantles of Monte Ferru and Monte Arci respectively, and 8 of the 

 small recent cones, the last manifestations of volcanic activity in 

 the island. The next two are of typical basalts of Pantelleria, 

 followed by analyses of the highly-scoriaceous lavas of the most 

 recent submarine eruptions in the neighbourhood of Pantelleria. 1 

 The next two analyses (13 & 14) are of the, as yet undescribed, 

 basalts of the island of Linosa : the former being a representative 

 of the solid lava-blocks found in the earlier phase of tuff-volcanoes, 

 and the latter of the more recent lava- and scoria-cones. Finally 

 15, 16, & 17 are the early analyses by Dr. H. Eosrstner, which are 

 tabulated for comparison with Nos. 9, 11, & 12. 



As regards the main constituents, these rocks present the fol- 

 lowing characters. Silica varies considerably, the highest figures 

 being found in the lavas of Sardinia, while in some of those of 

 Catalonia and Pantelleria they are rather low. Alumina is rather 

 low as a rule, and this constituent follows silica very closely, the 

 two rising and falling together. The oxides of iron, taken together, 

 are uniformly high, the totals varying from 10 to 13 per cent., 

 except in the Sardinian rocks, where somewhat lower figures are 

 met with. In every case ferrous oxide surpasses ferric oxide, the 

 amount of the former being frequently very great as compared with 

 that of the latter, as in Nos. 10, 12, & 14. Magnesia and lime are 

 not very high for basalts, the former varying considerably, while 

 the amounts of the latter are more constant, the lowest figures for 

 both being found in the Sardinian rocks. The alkalies, while not very 

 high, are sufficiently so in those rocks lowest in silica to give rise 

 to normative, as well as modal, nephelite, while the soda is uni- 

 formly dominant over the potash. 



Of the minor constituents, titanium-dioxide is the most notable. 

 This constituent is present in every case in very large amounts : 

 large, that is, for this substance, the average amount of which in 

 igneous rocks is 1 per cent, or less. Indeed, the higher figures 

 found in the table are unparalleled elsewhere, except in titaniferous 

 ores, as was mentioned above. It is lowest in the Sardinian 

 basalts, somewhat higher in those of Linosa, still higher in the 

 Catalonian rocks, and reaches its maxima in those of Pantelleria 



1 The specimen represented by No. 11 was very kindly given to ine by 

 Prof. E. S. Dana, while that represented by No. 12 was bought some years 

 ago of Mr. Butler, of Brompton Road, London, S.W. 



