30 SCIENCE PROGRESS. 



small island Vulcanello consisting, as Backstrom has recently 

 shown, of leucite-basanite, though quite different from the 

 Vesuvian lavas (7). The Etna basalts have a somewhat 

 peculiar composition. Besides the augite-trachytes, some 

 with sodalite, near Naples, and the more singular basic 

 variety with olivine on Ischia, many curious trachytic rocks 

 occur at various points from Monte Amiata in Tuscany to 

 Monte Ferru in Sardinia. The Spanish and African parts 

 of the province have been less completely investigated, but 

 we may recall among the Cabo de Gata rocks the peculiar 

 glassy lava with the composition of a lamprophyre, to which 

 Osann has given the name verite (8). 



The laws governing the local distribution of the several 

 rock-types within such a province offer a problem on which 

 as yet little light has been thrown. Lang has attacked it 

 from the chemical standpoint, laying special stress upon the 

 relative proportions of the alkalies and lime in the chemical 

 analyses of the lavas and tuffs (9). He gives reasons for be- 

 lieving that the numerous volcanic centres in the neigh- 

 bourhood of the Bay of Naples are situated on three main 

 lines of fissure. The rocks in each set show a considerable 

 range of composition, but have common characteristics in 

 the respect indicated. One fissure or set of parallel fissures, 

 which he calls the Appenine, runs parallel with the Appenine 

 Chain to the Alban Hills and beyond. The other two, 

 named the Pontine and the Tyrrhenian, take more westerly 

 courses, crossing one another obliquely in the Ponza Islands. 

 The fissures, the existence of which is thus inferred, are of 

 course a different order of phenomenon from the dyke- 

 fissures to which " massive " eruptions have been ascribed. 

 If established, their different directions and the distinctness 

 of the associated sets of rocks point to different dates for the 

 activity of the several fissures. Indications of such fissures, 

 or at least of secondary directing lines of volcanic activity, 

 are to be discerned in other provinces ; for instance, as 

 Washington has shown in the .^gean ; and they have 

 been postulated by many writers on the phenomena of 

 vulcanicity. 



One feature which can scarcely be overlooked in the 



