240 Washington — Catalan Volcanoes and their Bock*. 



Apart from the silica of the Castellfnllit camptono.se (feld- 

 spar-basalt), which is about 3 per cent higher than in any of 

 the other rocks, all these analyses reveal a remarkable uniform- 

 ity as regards all the constituents. With the exception just 

 noted, silica is rather low and varies only between 43-64 and 

 44*82, alumina between 12*48 and 15*51, the total iron oxides 

 between 10'87 and 12*45, magnesia between 8*03 and 10*85, 

 lime between 7*99 and 9 - 91, soda between 2*99 and 4*04, potash 

 between 1*54 and 2*57, titanium dioxide between 3*83 and 4*92, 

 and phosphoric pentoxide between 0*45 and 0*74. The only 

 variation of moment is that in the relative amounts of ferric 

 and ferrous oxides, the former being between 2*35 and 6*40, 

 and the latter between 5*52 and 8*84, the maximum for ferric 

 oxide and the minimum for ferrous being found in the same 

 specimen (III), and apart from this the figures being fairly con- 

 cordant. As noted above, it would seem that the conditions 

 of extrusion had some influence over these relations, the ratio 

 of ferrous to ferric oxide being in general higher in the mas- 

 sive flows and lower in the scoriaceous lava, this being due pre- 

 sumably to the more favorable conditions for oxidation in the 

 latter. A somewhat similar state of affairs has been observed 

 in the basalts of Sardinia, Pantelleria and Linosa, as will be 

 described in subsequent papers. 



Apart from this general uniformity, and the chief charac- 

 ters of the main constituents, such as the rather low silica and 

 alumina, the high iron oxides, moderately high magnesia and 

 lime, and rather high soda (for salfemic rocks) and low potash, 

 the most striking feature is the very large amount of tita- 

 nium dioxide. While most or all of the figures for this con- 

 stituent here given can be duplicated in analyses of igneous 

 rocks from other localities, yet the vast mass of analyses hith- 

 erto published reveal scarcely a single district where the figures 

 for titanium dioxide are uniformly so high as those of Catalo- 

 nia. Aside from analyses of my own of rocks from Pantelle- 

 ria and Linosa, and not considering titaniferous ores, the only 

 ones which show figures surpassing those here given are those 

 of the melilite-basalts of the Hegau by Grubenmann, which 

 are all dofemanes and rich in perofskite ; while figures approx- 

 imately the same as those for Catalonia are seen in analyses of 

 salfemanes and dofemanes from German Kamerun, Magnet 

 Cove, Brazil, and some localities in New Englarvd. 



Of the other minor constituents few call for any special 

 notice. Phosphoric pentoxide is fairly but not abnormally 

 high, zirconia seems to be present merely in traces, as is also 

 true of baryta and strontia, while manganese is present in the 

 usual small amounts. Nickel is invariably present apparently, 

 and was determined in two cases, the figures being rather high 



