2 Prof. J. W. Judd—The Lavas of Krakatoa. 
are frequently described as “enstatite-andesites” or “ hypersthene- 
andesites.” 
Now these andesites of Krakatoa have been very carefully 
investigated, both by chemists and mineralogists, during the last 
four years. The memoirs of Richard,’ Renard * Sauer,® Reusch,* 
Oebbeke,® Von Lasaulx,® Carvill Lewis,’ Joly,® Tear, 9 Waller,!® and 
especially of Verbeek, Retgers, and Winkler," leave us little imadeed 
to be desired in this respect, We have not only a number of inde- 
pendent analyses of the rocks themselves, but also of each of the 
minerals contained in them; these having been isolated by the 
refined methods of modern petrography. Hach of the minerals too 
has been submitted to searching optical investigations, so that there 
are few rocks of which we can be said to know the chemical com- 
position and mineralogical constitution more thoroughly. 
_ It very fortunately happens that there are several other rocks 
belonging to the same general type which have also been investigated 
in the same thorough manner. Those that I have especially chosen 
for comparison are (1) the ancient and modern lavas of Santorin 
which have been studied by Zirkel, Karl von Hauer,” and especially 
by Prof. Fouqué.’ (2) The lava of Buffalo Peaks, Colorado, for the 
description of which we are indebted to Mr. Whitman Cross “ of the 
U.S. Geological Survey, and (3) the more ancient but very similar 
lavas of our own Cheviot Hills, which have been so carefully studied 
and described by Mr. Teall * and Dr. Petersen.’ 
Now these rocks, coming from such widely different localities, all 
agree in the minerals of which they are made up. They all include 
crystals of several species of plagioclastic felspar, the most basic or 
those containing a large per-centage of lime being very abundant; 
there are in all of them two pyroxenes, namely, ferriferous enstatite 
and augite, the former being present in greatest quantity ; and they 
all contain magnetite with some ilmenite. In addition to the porphy- 
ritic crystals of these minerals, there is a base or ground-mass some- 
times consisting of a nearly pure glass, at other times of glass which 
has undergone a greater or less amount of devitrification, whereby it 
has passed into a more or less perfectly stony mass. 
1 Comptes Rendus, Seance du 19 Novembre, 1883. 
2 Bull. de l’Acad. Royal de Belgique, 3re ser. t. vi. (1883). 
3 Berichte der Natur, Gesellsch. zu Leipzig, 1883, p. 87. 
4 Neues Jahrb. fiir Min. etc. 1884, bd. 11. 
5 Tbid. 1884, bd. ii. p. 32. 
6 Sitze. d. niedersch. Gesch. in Bonn, Sitz. vom 3 December, 1888, 
7 Proc. Acad. Se. Philadel phia, 1884, p. 185. 
8 Roy. Dublin Soe. n.s. vol. iv. p. 291. 
9 “Ta Nature,’’ 1gme. Année (1885), p. 378. 
10 Birm. Nat. Hist, and Microscop. Soc. Rep. and Trans. for 1883, p. vi (March, 
1884). aM Krakatau, pp. 185-824. 
12 Neues Jahrb. fiir Min. etc. 1866, p. 769. 
18 Santorin et ses Eruptions, 1870. 
M4 Bull. U. 8. Geol. Survey, No. 1 (1888). \\ 
15 Grou. Maa. Ser. II. Vol. X. pp. 106-109 and 252-263. 
16 Mikroscopische und Chemische Untersuchungen am Knstatitporphyrit aus den 
Cheviot Hills, Kiel, 1884. 
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