26 HENRY S. WASHINGTON 



It is of special additional interest to note that, analogously to 

 Pantelleria, the SomaH lavas are divided into a large group of 

 pantellerites, rhyolites, and trachytes, with silicity from 76.0 to 

 66 . 5 per cent, and a smaller of basalts, the silicity of which runs 

 from 50.1 to 46.2; and that there are no phonolites, kenytes, or 

 other intermediate types here. A further resemblance is that the 

 basalts are "always the most recent of the volcanic series to which 

 they belong." The general silicity of the Somali rocks is higher 

 than that of Pantelleria. 



Another analogous region is that of British East Africa, includ- 

 ing the Rift Valley, described by Prior,' and Mt. Kenya described 

 by Gregory.- Both of these geologists call attention to the resem- 

 blance of some of the more silicic lavas to those of Pantelleria. 

 These highly sodic rocks are accompanied by plagioclase basalts 

 of ordinary types, though no analyses were made of them. At 

 Mt. Kenya these basalts are the last eruptive products. This 

 region differs from Pantelleria and Somali in the abundance of 

 phonolite, kenyite, and other nephelite-bearing lavas. 



Similar rocks have also been described from Eritrea, Abyssinia, 

 Masai Land, Madagascar, Aden, and Sokotra; and farther away 

 they have been met with in Japan, Australia, New Zealand, Ger- 

 many, and Texas. 



Closely allied to the Pantellerian lavas, both chemically and 

 modally, but of paleotypal habit and occurring as intrusive dikes 

 and other bodies, are grorudites, solvsbergites, and paisanites of 

 Greenland, Norway, Massachusetts, Texas, and elsewhere. 



It is a noteworthy fact, bearing on the discussion of the norm 

 on a previous page that sodium metasilicate usually appears in 

 notable amount in the norms of these rocks which carry arfvedsonite, 

 while it is either less or absent in the norms of those which contain 

 only aegirite or aegirite-augite. 



Attention may also be called to a feature of igneous rocks which 

 carry aegirite or sodic hornblende, which is in accord with the prin- 

 ciples adopted in establishing the norm. This is that such rocks 



^ G. T. Prior, Min. Mag., XIII (1903), 228. 



= J. W. Gregory, Q.J.G.S., LVI (1900), 205. No analyses given. 



