600 J. V. LEAVIS OEIGIX OF PILLOW LAVAS 



diabase masses of Mont Genevre evidence of the rolling over of the lavas 

 among themselves ; and we are led to regard the presence of variolitic selvages 

 throughout such great thicknesses of rock as largelj" due to movements taking 

 place within a crater.'' 



Comparison is made with the movements of lava in the crater of Kilauea, 

 the Mont Genevre rock being considered the equivalent of "only the lower 

 layers of the volcanic caldron," the upper portions having been removed 

 by erosion. 



Eocks described as 'S ariolitic tuffs'' are associated with the diabase, but 

 "they may, indeed, be friction-breccias or lavas broken up while viscid or 

 volcanic tuffs.^' Spherical "bombs" are abundaiit, coated with variolite 

 and contained in a matrix that is regarded as ash. The masses have a 

 radial columnar structure, which gives a tesselated appearance on the 

 surface. The largest measured TO by 43 by 45 centimeters. Small frag- 

 ments are often scoriaceous and very angiilar and the matrix contains 

 many particles and fragments of basic glass. Compared with the rugged 

 aa flows of Hawaii, these beds are found dissimilar. "Xeither the ar- 

 rangement of the masses nor the globelike bombs correspond with the 

 features so clearly described and figured by Professor Dana," and the 

 authors are led to consider these deposits as the products of true explosive 

 action. 



Zaccagna-^ has described a spheroidal diabase, with variolitic crusts 

 identical with that of Mont Genevre from Monte Yiso. in the western 

 Alps south of Mont Genevre. He considered the spheroidal forms, how- 

 ever, to be the result of weathering. 



"Queste roccie verdi constano in massima parte di serpentina con qualche 



intercalazione di aufiboloscisto e di diabase Auche la diabase che 



trovasi nelle vicinanze inserita nel calcescisto e identica a quella eocenica ed 

 ha come questa la particolarita di foruire colla decomposizione delle masse 

 sferoidali. Non di rado nelle masse testacee della roccia in decomposizione 

 trovasi una crosta variolitica identica a quella. della massa del Mont Genevre." 



Platania-- has described the globular basalt at Acireale. on the eastern 

 coast of Sicily, where two types of structure are found : ( 1 ) Large, with 

 radial jointing, forming prismatic wedges, and (2) variable dimensions, 

 with concentric cleavage, some of which inclose foreign rocks. Both are 

 closely associated with tuff beds, and the globes are commonly slightly 

 deformed, as if they had been pressed together while yet pasty. The crusts 

 are glassy and the interspaces are occupied by clay and tuff. The sphe- 



21 D. Zaccagna : Sulla geologla delle Alpi occidentall. Boll, del R. Comlt. Geol. d'ltalla, 

 vol. xvlU. 1887. p. 387. 



~ G. Platania : Geological notes of Acireale. The South Italian Volcanoes, ed. by H. J. 

 .Tohnston-Lavis. Naples, 1891, pp. 37-44. 



