70 DE. H. S. WASHINGTON ON THE TITANIFEEOT7S [Feb. I907, 



of a comagmatic region (petrographic province) extending in a 

 rather narrow zone from Linosa on the south-east, north-west- 

 ward through Pantelleria and Sardinia, and possibly through the 

 volcanoes of the southern French littoral to Catalonia. The 

 possibility of the further extension of this zone in a southerly 

 direction, along the eastern coast of Spain, will be discussed 

 subsequently. 



For the present, we must confine our attention to the most 

 femic rocks of the region, the basalts in common parlance, for the 

 study of which numerous specimens and thin microscopic sections, 

 and some twenty chemical analyses, are available. Only brief petro- 

 graphical descriptions need be given here, and elaborate discussion 

 of the analyses is omitted. But attention may be specially called to 

 the mineralogical similarity among the basalts, which obtains all 

 along the line : labradorite, augite, and olivine being uniformly the 

 predominant and essential minerals, with accessory but constant 

 amounts of a titaniferous magnetite and apatite, and in some cases 

 accompanied by subordinate amounts of nephelite. Hornblende 

 and biotite are either entirely absent from the salfemanes of the 

 region, or present in a few rare types. The concordance in 

 chemical composition is most noticeable in the low alumina, the 

 abundance of the iron-oxides (ferrous oxide being greatly in excess 

 of ferric), the relatively rather high amount of soda, the uniformly- 

 high figures for titanium-dioxide, and the almost constant presence 

 of notable quantities of nickel. 



Owing to the incompleteness of the earlier analyses of the rocks of 

 these localities which have been examined chemically, such as those 

 of Monte Ferru by Prof. Dcelter and of Pantelleria by Dr. Fcerstner, 

 and the total lack of analyses of the rocks of Catalonia, Linosa, and 

 of most of the Sardinian occurrences, the petrological connection 

 between these localities and the peculiar chemical features of their 

 basalts have not been suspected until recently. The first, and so far 

 the only, petrographer to note their highly-titaniferous character 

 was Foerstner, 1 who found 5 - 86 per cent, of titanium-dioxide in the 

 basalt of the island of 1891 near Pantelleria, and who suggested 

 that this constituent was probably present in similar amounts in 

 the basalts of Pantelleria and Graham's Island (1831), as well as 

 in those of Etna. More recently, the probability of some relation- 

 ship between the lavas of Sardinia, Pantelleria, and (possibly) 

 Linosa was pointed out by me, 2 although the possibility of any 

 connexion with the Spanish rocks was not thought of. 



II. Peteogeaphical Descriptions. 



The salfemanes (basalts) are, with very rare exceptions, of 

 common types, presenting no very peculiar or specially-noteworthy 

 features, either in the hand-specimen or under the microscope. In 



1 Tscherm. Min. Petr. Mitth. vol. xii (1891) p. 520. 



2 Am. Journ. Sci. ser. 4, vol. viii (1899) p. 293. 



