180 Editorial Comment. 
to the development of crystals as above described is the fol- 
lowing : 
"The labradorite-andesite in which these crystals occur is 
one of an old series of felstone-lavas belonging to the earliest 
period of eruption in the Mull volcano. The lava-stream was 
exposed to weathering and denudation for a long time, suffi- 
cient to allow the mechanical injury and partial kaolinization. 
Subsequently this old lava was buried to the depth of several 
thousand feet by the later welling out of basaltic and other 
lavas. The consequence was that the mass was placed in con- 
ditions favorable to the development of the felspar crystals 
They renewed their youth and recommenced growth." 
In a third paper also in the Quarterly Journal for May, Prof. 
Judd put forth some results of a long study of the igneous 
rocks of the "Western Isles of Scotland. Three principal points 
are insisted on : 
1. That the plutonic, holocrystalline rocks of the Western 
Isles (granites and gabbros) are only the extreme terms of 
two series which pass by almost imperceptible gradations into 
the opposite extremes of volcanic pitchstones and tachylites. 
2. That the enormous sheets of igneous rocks once covering 
this area and now indicated only by scattered outliers issued 
from numerous centers of eruption of which five at least are 
still recognizable at Mull, Ardnamurchan, Rum, Skye and St. 
Kilda. 
3. That these lava-beds and sheets of crystalline rock of all 
kinds are entirely of Tertiary age and of subaerial origin. 
Some of these conclusions will surprise geologists who have 
not followed the course of recent petrological investiga- 
tions. But Prof. Judd's propositions are supported with a mass 
of evidence that carries conviction. As he says : "The evi- 
dence is irresistible that gabbros graduate insensibly into 
dolerites and dolerites into basalts and basalts into tachylites." 
The granites also merge insensibly through "granophyric forms 
into acid lavas and pitchstones." 
These gabbros and basalts have been attributed by various 
writers to earlier dates, such as the Jurassic or even to the 
Laurentian, chiefly on the evidence of their composition 
and of their intimate association with the granites whose 
antiquity was assumed. The whole form "one great contempo- 
raneous series of rocks which as a whole overlies and is 
