1894.] Petrography. 603 
of all the dykes is practically the same. Their mineral composition 
and structure, however, vary. In the largest dykes the number of 
constituents discovered is much greater than in the smaller ones. They 
embrace the usual diabase components with the addition of a light col- 
ored sahlitie pyroxene differing from the sahlite of Sala in the value 
of its optical angle. In the Brazil mineral E,—32? 39’, while in the 
Sala mineral it is 112? 30'. It is the oldest constituent of the rock 
after magnetite, and, consequently it is that which approaches most 
nearly to being idiomorphic. The structure of the large dykes is 
gabbroitic and ophitie, whereas that of the small ones is porphyritic 
and hyalopilitie, with the pyroxene figuring as the phenocrysts. 
Quartz is not uncommon in the coarser rocks and granophyric inter- 
growths of quartz and feldspar are frequently met with. 
The New Island off Pantelleria—A Correction.—In these 
notes for December® last, the statement was made concerning the 
material of a recent eruption near Pantelleria, that it consisted of loose 
blocks and of lava. Mr. G. W. Butler of Chertsey, England, cor- 
rects thisstatement in a recent letter to the writer and declares that the 
new island formed during the ernption was composed entirely of loose 
scoriaceous bombs, which disappeared a short time after the eruption 
ceased. ; 
Petrographical Provinces.—Iddings*® gives a brief and, conse- 
quently, a tantalizing account of the old voleano of Crandall Basin in 
the Absaranka Range of Mountains in the Yellowstone National Park, 
that has been eroded in a manner to give a good section of the cone 
with the dykes and flows radiating from it. The different rock types 
mentioned in the paper are simply alluded to, a full account of them 
being promised later. The author's conclusion from his study is to the 
effect that we have here proof that the texture of rocks and their[min- 
eral composition is more directly dependent upon the rapidity with 
which the rocks cooled, than upon the pressure to which they were 
subjected during their solidification. The differentiation of rock mag- 
mas is also well shown in the case of the volcano studied by the pro- 
duction of many individual rock types. 
Upon comparing thirty-nine of the best analyses of rocks occurring 
in the eruptive areas around the Bay of Naples, Lang? concludes that 
SAMERICAN NATURALIST, Dec, 1893, p. 1088. 
"Cf. also G. W. Butler; Nature, April 21, 1892. 
‘Jour. Geol, Vol. 1, p. 606, 
?Zeits, $0 deutsch. geol. Ges, XLV, p. 177. 
