Editorial Comment. 179 
supporting the belief that "all bodies can mix when the pres- 
sure exceeds a certain value." 
This subject has been developed at greater length in one 
direction by thesame author in the Quarterly Journal for May 
1889, where he describes a singular example of the growtli of 
the felspar crystals (near labradorite) inaporphyritic andesite 
from Dun da Gu ' in the island of Mull. 
The original crystal was much weathered before its enlarge- 
ment began so that it exhibited cracks, corroded surfaces, 
planes of kaolinization and sometimes actual fracture. The 
added portion and the filling of the cracks show their second- 
ary nature by their behavior under polarized light. "The 
inner and outer parts do not extinguish simultaneously when 
the section is rotated between crossed nicols but after the 
position of extinction of the central core has been passed a 
dark zone makes its appearance around the central mass and 
as rotation goes on this dark zone passes slowly and gradually 
outward through the surrounding fringe." 
That the addition was made at the expense of the unstable 
vitreous matrix is shown by the fact that where two crystals 
touch one another no enlargement has occurred. The change 
in the angle of extinction is so gradual and extensive that 
Prof. Judd says he is led to the conclusion that some of these 
crystals liave a fringe of secondary material which as we pass 
outward corresponds to every intermediate stage through the 
andesine and oligoclase series, and sometimes approaches if it 
does not actually reach the albite limit. 
These changes in the constitution of the crystal during its 
successive stages of enlargement are attributed by the author 
to the tendency of the more basic minerals to separate from 
a magma before the more acid ones,whereby the lime is grad- 
ually abstracted and the crystal tends to pass from a basic 
lime-felspar to an acid alkali-felspar or even to quartz. 
The sequence of events which in Prof. Judd's opinion has led 
• The most enthusiastic admirers of the Gaelic tongue, even Prof. 
Blackie himself would scarcely recommend it for a universal language 
on account of the simplicity o! its spelling. In the paper quoted Prof. 
Judd kindly giveB his remlers a very necessary kev to the pronuncia- 
tion of the names of the places mentioned. Our readers may judge for 
themselves how necessary is this help. 
Dun-da-Gu is spelled Pun-da-Ghavithe. 
Sarsta Beinn " S'Airde Beinn. 
BeinnUaig " Beinn-na-Duatharacli. 
