Vol. 63.~] BASALTS OF THE WESTERX MEDITERRANEAN. 77 



IV. Classification of the Hocks. 



The classification of these lavas according to the prevailing 

 systems has been sufficiently indicated in the foregoing pages. For 

 the most part, they are felspar-basalts, with fewer nephelite-basalts, 

 these last occurring especially in Catalonia and not having been, 

 as yet, definitely determined from the other districts. These basalts 

 are usually olivine-bearing, although in Sardinia olivine-free types 

 are rather common. 



The classification according to the quantitative system is based 

 on the figures furnished by the analyses, and on the calculated 

 norms, which latter are shown in the appended Table II (pp. 74-75). 

 In this the norms are numbered as in Table I of Analyses, and the 

 symbols representing the class, order, rang, and subrang are given 

 in each case below. 



The great majority of the basalts lie within the salfemane class, 

 the exceptions being some of the Sardinian basalts and that of 

 Graham's Island, which are in dosalane, these being distinctly higher 

 in normative felspar, especially albite and anorthite, than the others. 

 Outside of Catalonia, where normative (and modal) nephelite is so 

 abundant as to cause some of the types to fall in the sixth order, 

 with felspars dominant over nephelite, the order is uniformly the 

 fifth ; that is, the quantities of either quartz or nephelite are negli- 

 gible as compared with the felspars. The rang is almost as uniformly 

 the third, with alkalies and salic lime in about equal amounts, and in 

 only two cases are the alkalies dominant over salic lime (Nos. 1 & 8).. 

 The relation of the alkalies is very constant, soda being dominant 

 over potash in every case, so that the subrang is invariably the 

 fourth. 



Although, in the salfemanes, the femic x constituents form about 

 one half of the rock, their relations, as expressed in the minor 

 divisions of grads and subgrads, may be disregarded in the present 

 brief discussion, as unnecessarily prolonging it, and introducing 

 what may seem to be a superfluous refinement into the present 

 introductory and little tried stage of the new classification. 



As illustrative of the correlation of the two systems of classifica- 

 tion, a few points may be dwelt on very briefly. While all those 

 rocks, which are free from nephelite, would be called basalts in 

 the prevailing systems, it will be observed that the distinctions be- 

 tween them are more numerous according to the quantitative system. 

 The basalts of Pantelleria and of Linosa are uniformly in camptonose 

 (in salfemane), as are also many of those of Catalonia. On the 

 other hand, many of those of Sardinia fall in andose or akerose in 



1 It is to be remembered that the term ' femic ' applies only to the standard, 

 non-aluminous minerals, like ideal diopside, hypersthene, olivine, or magnetite. 

 Such ' ferromagnesian ' minerals as augile, hornblende, or biotite, which contain 

 alumina, are termed ' alferric,' and their molecules are resolved into salic and 

 femic components in the calculation of the norm. It may thus happen that a 

 rock with augite very much more abundant than plagioclase (and hence at first 

 glance apparently dofemic) is actually in the salfemane class. 



