360 Dr. A. Wilmore—Uralite and other Amphiboles. 
in this manner it is actually found to exhibit a series of twin-lamellee 
arranged parallel to the so-called gliding-planes. 
There is still a third and even more subtle set of structure-planes in 
crystals, those, namely, for which the name of solwtcon-planes has been 
proposed. 
In the section dealing with the ‘etiology’ of minerals (the causes 
by which the existing forms, capabilities, and position of minerals and 
rocks have been determined) Professor Judd compared the change from 
unstable monoclinic sulphur—by a pressure of 5000 atmospheres—to 
the stable rhombic form, and that of yellow mercuric iodide, by simply 
rubbing, into the stable red tetragonal form, with the ‘“‘ paramorphic 
change of pyroxene into hornblende, which is so frequently exemplified 
in the earth’s crust’’. 
In the next paper to be noticed he explained his now well-known 
theory of schillerization, and showed the connexion between this 
process and the planes of discontinuity in crystals.! This paper is of 
importance in connexion with uralitization, as it deals to some extent 
with augite, diallage, and the amphiboles, and the changes set up in 
the pyroxenes. 
The difference between minerals found at great depths and the 
same minerals found near the surface is sometimes original—due to 
pressure and slow growth—sometimes secondary, such as the bands 
of fluid enclosures, the avanturine structure, and the chatoyant 
phenomena. 
The same phenomena, but more closely connected with the subject 
of this paper, were further elucidated in a paper by Professor Judd in 
1890.2, In that paper he reviewed the work of Miigge on the 
diopsides of Ala, of Phillips and Teall on the Whin Sill augites, and 
showed that augites in the Tertiary basalts of Ardnamurchan present 
the same features, viz. lamellar twinning parallel to the basal plane 
(001) and not parallel to the orthopinacoid (100). According to the 
work of Miigge this may have been caused by pressure. The lamellar 
twinning or parting of diallage, parallel to the orthopinacoid (100), 
is due to solution acting along the solution-planes. 
There is one other paper by Professor Judd which should be included 
in this important series. This paper deals with a pyroxene-felspar 
rock at Oodegaarden, near Bamle, in Norway. This rock has been 
converted into hornblende-scapolite rock. MM. Fouqué and Michel- 
Lévy had shown that by fusion (with a trace of sodium fluoride) 
and slow cooling this hornblende-scapolite rock is, in turn, converted 
into a pyroxene-felspar rock. 
The change of felspar into scapolite may be followed step by step. 
The solvent which attacked the felspar crystals along their solution- 
planes, and which acted under statical pressure, contained sodium 
1 « On the relation between the Solution-planes of Crystals and those of Secondary 
Twinning, etc.: a contribution to the Theory of Schillerisation ’’; Min. Mag., 1887, 
vol. vii, pp. 81-93. 
2 «On the relation between the Gliding-planes and the Solution-planes of Augite”’: 
Min. Mag., 1890, vol. ix, pp. 192-6. 
3 «On the process by which a Plagioclase Felspar is converted into a Scapolite ”’: 
Min. Mag., 1889, vol. viii, pp. 186-98. 
