LINOSA AND ITS ROCKS 



21 



The occurrence of gypsum in vesicles of basalts is not mentioned 

 in the standard works of Zirkel, Rosenbusch, Roth, Iddings, and 

 Levy and Lacroix, but its presence has been recorded in the vesicular 

 lavas and the fumarole products of Vesuvius^ and Etna,^ and it is also 

 mentioned as present in the boihng water of the crater lake of Graham's 

 Island ;3 though, on the other hand, no mention is made of its presence 

 at some other volcanoes, as Santorini and those of the Hawaiian 

 Islands. It may also be mentioned that I did not find it in the very 

 similar lavas of the Catalan volcanoes, nor is it recorded by Fernandez- 

 Navarro in his very complete description of these lavas.^ It also 

 seems to be absent from the basalts of Pantelleria, not being mentioned 

 by Foerstner,^ nor having been observed by me. 



CAMPTONOSE (FELDSPAR- BASALT), IL FOSSO TYPE 



Megascopic characters. — In general these lavas are rather lighter 

 in color than those of the preceding type, being mostly light to rather 

 dark gray, decidedly black lava being rare. They are also more apt 

 to be compact, and highly vesicular forms are less often met with. 

 While they are porphyritic, phenocrysts are less abundant, this being 

 especially noticeable in those of feldspar, which are very few, somewhat 

 tabular, but furnishing rounded outhnes in the hand specimen, and 

 are usually rather large, up to 10"^"^ long and 5"^°^ wide, though very 

 small and inconspicuous ones are also present. The phenocrysts of 



1 J. Roth, Der Vesuv, Berlin, 1857, P- 369; ^i^d J. L. Lobley, Mount Vesuvius, 

 London, 1889, p. 287. 



2 Sartorius von Waltershausen, Der Aetna, Leipzig, 1880, Vol. II, p. 525. 



3 H. Abich, Vulkanische Erscheinungen, Braunschweig, 1841, p. 75. 



4Cf. " Formaciones volcanicas de la Provincia de Gerona," Mem. Soc. Espan. 

 Hist. Nat., Vol. IV, 1907, pp. 437-43. 



s E. Foerstner, Boll. Com. Geol. Ital., 188 1, p. 533. 



