GEOLOGY — WASHINGTON. 173 



microscopic examination of the thin sections, so as to insure the selection of 

 representative specimens for analysis. The number of analyses so far made 

 of these rocks is twenty-four, with three of minerals occurring in them. 

 The rock analyses are, for the most part, of the more femic types (basalts), 

 with fewer of the more salic ones. This analytical work indicates that the 

 lavas of Catalonia are closeW similar to the more femic ones of the other 

 three districts, and discloses the existence in the western Mediterranean 

 basin of a hitherto unrecognized comagmatic region (petrographic province) . 

 This forms a volcanic zone extending from I^inosa, on the southeast, through 

 Pantelleria and western Sardinia, to Catalonia, the volcanoes of the French 

 Mediterranean littoral (as those of Agde and Montpellier) probably also 

 belonging to it, with a possible extension down the east coast of Spain, and 

 also possibly in Tripoli south of Linosa. The most striking feature of this 

 region is the richness of the more femic rocks in titanium, the figures for 

 TiOj found in the analyses being higher than those shown by any other 

 known region of igneous rocks, other than some titaniferous ore bodies pro- 

 duced by magmatic differentiation. It may be mentioned that the figures 

 for TiO., in these basalts vary from 2.64 to 6.88 per cent. Other chemical 

 features of the region are the high amounts of iron oxides, especially fer- 

 rous, the usually rather low alumina, magnesia, and lime, the dominance of 

 soda over potash, and the prevalence of nickel in, for this constituent, rather 

 large amounts. The analyses which were made of Pantellerian lavas, as 

 well as those of the lavas of Graham's Island, and of that of 1891 in the 

 vicinity, substantiate the earlier ones of Foerstner in their general features, 

 though being more complete they introduce some very important corrections. 



The lavas of Catalonia and Linosa were found to be salfemanes without 

 exception, belonging to the subrangs camptonose, limburgose, and monchi- 

 quose, or basalts and nephelite-basalts in the prevailing classifications. 

 Those of Sardinia and Pantelleria are much more varied — so much so as to 

 preclude their enumeration here. 



The minerals analyzed include an augite and an olivine from Monte Ferru 

 and a hornblende from Linosa. The two former are not specially note- 

 worthy in themselves, though of interest in connection with the rocks in 

 which they occur, but the hornblende is remarkable, the figure for TiOj (8.47) 

 being the highest yet recorded for this mineral. It is probably related to 

 the kaersutite of Greenland. A peculiar and possibly new mineral was 

 found in the crevices of rhyolite at Monte Arci, forming yellow, translu- 

 cent, hexagonal prisms, and will be investigated later. 



The study of the material mentioned above will extend probably over two 

 years, and the results will appear from time to time in the American Journal 

 of Science, the Journal of Geology, and probably elsewhere. It is estimated 

 that at least 70 analyses must be made for proper discussion of all the rock 

 types of this region. 



