Dr. A. Wilmore—Uralite and other Amphiboles. 309 
rate in the majority of cases. Rose’s original suggestion, though 
enly touching one aspect of the possible chemical changes, was 
nearer the truth. ce 
In 1880 yon John described Flysch gabbros from Bosnia (‘‘ Uber 
Kryst. Gest. Bosniens”’?: Jahrb. der k.k., etc., Vienna, 1880), and he 
stated that the kind of secondary hornblende produced depends upon 
the composition of the original pyroxene. Brown hornblende results 
from the alteration of dark diallage, but green hornblende from the 
alteration of green diallage. The secondary brown hornblende is very 
strongly dichroic, but the hornblende derived from the light-green 
diallage is fibrous and almost colourless. The hornblende passes by 
further change into chlorites. 
Cohen (Sammlung von Mikrophot. von Mineralien u. Gest., Stuttgart, 
1884) illustrated the development of uralite in his pl. xlvi, figs. 1-4. 
Fig. 1 shows the beginning of uralitization in the periphery of a crystal, 
and is taken from a micro-section of the so-called uralite-porphyry 
from Predazzo in the Tyrol. Fig. 2 shows the beginning of uralitiza- 
tion in the central part of a crystal, and is from a ‘ proterobase’ 
from near Audlan in the Vosges. Fig. 3 shows complete uralitization ; 
section parallel to the vertical axis, and is again from the uralite- 
porphyry of the Tyrol. Fig. 4 shows complete uralitization ; section 
nearly at right angles to the vertical axis. It is from the so-called 
uralite-porphyry of Miask in the Urals. The form is augite, the 
cleavage that of hornblende. 
An important work is Lehmann’s study of the crystalline schists 
of Saxony, etc.1 In ch. xi, p. 191, which deals with gabbros 
and amphibole rocks (Amphibolgesteine), he mentioned a series of 
secondary minerals, among which are amphibole, saussurite, magnesia- 
mica, ete. He described the change from pyroxene to amphibole as 
one of paramorphism. Later, p. 197, he described amphiboles of 
secondary origin, which are sometimes like smaragdite, sometimes like 
actinolite. The amphiboles and other secondary minerals are due 
in part to pressure. An important observation is that the formation 
of magnetite often accompanies that of amphibole derived from 
hypersthenes rich in iron. 
We now come to the very important series of contributions made by 
Professor Judd during the years 1885-90. Though not the earliest of 
the series it may be well to take first the Presidential Address to the 
Geological Society of London in 1887.2, This address deals with the 
morphology, physiology, chorology, and etiology of minerals. In 
the section treating of the physiology of minerals Professor Judd 
pointed out the importance of recognizing the different structure- 
planes of crystals. The most obvious of these are the cleavage-planes. 
These, however, are not the only latent structure-planes in crystals. 
Brewster, Reusch, and Pfaff had shown long ago that when crystals 
are subjected to pressure in certain directions their molecules appear 
to glide over one another along certain definite planes within the 
crystal, and if we examine optically a crystal which has been treated 
1 Untersuchungen wiber die Entstehung der Althrystallinischen Schiefergesteine, 
Bonn, 1884. 
* Quart. Journ. Geol. Soc., vol. xliii, p. 68 et seq. 
