430 MR. EDWARD GREENLY ON THE [ Aug. 1902, 
lavas often arise as local “ knots” during the latest consolidation of the rock, and 
include the pre-existing structures. The brown tachylyte between the bands of 
small spherulites is in places distinctly perlitic, and its vitreous character is well 
preserved. The rock is generally more glassy than crystalline; but the more 
lithoidal bands show the tufted aggregates of microlites, and even the ‘‘pseudo- 
crystallites” that are so characteristic of true variolite.’ (See Pl. XVI, fig. 2.) 
‘No. 4, 1899.—This rock also has retained its glassy characters far better than 
is the case in typical variolites. In this, it resembles the selvage of the variolite 
of Annalong (Co. Down). It has been brecciated during its viscid flow, like the 
obsidian of the Rocche Rosse at Lipari, and spherulitic matter has collected 
from the matrix in which the consolidated angular fragments of brown glass 
were carried onward. Banded structure, often very delicate, resulted from the 
movement of the mingled mass; and then the whole lava was again broken up, 
perhaps by earth-movement. The interstices between the fragments that were 
thus formed are now filled by chlorite, and what appear to be minute radial 
aggregates of chalcedony. 
‘The angular patches that look ike pseudomorphs after olivine, occurring in 
the original glass and in the larger spherulitic aggregations, are of puzzling 
nature, since they seem identical with the minute spherulites that were deve- 
loped at an early stage of the consolidation ; every intermediate type, judging 
by outline, occurs between the tiny rounded spherulites and the angular little 
bodies that look like crystals. Even the latter are isotropic, and I fancy that 
they are spherulites actually passing into crystalline granules, but of what nature 
I cannot determine. Such an occurrence is a rare one, but is paralleled by the 
outlines assumed, before complete differentiation of the crystalline matter from 
the matrix, by the “‘spots” in some ‘spotted slates” produced by contact- 
metamorphism. 
‘This rock has, I fake it, a complex history, the first brecciation occurring 
while it was still a viscid mass, and a certain blending thus occurring between 
the firmer glass-fragments and the new material that gathered from the matrix 
round them. ‘The second brecciation affected both the old fragments and the 
matrix, which by this time had consolidated against them.’ 
In the Newborough sand-hills, the variolite is apt to occur in zones 
which are approximately parallel, and generally near to the margin 
of the ‘ pillows,’ though in some of the smaller spheroidal bodies 
varioles are pretty evenly distributed throughout. This is the mode 
of occurrence of the famous variolite of Mont Genevre," where 
the diabase has pillowy structure of the same kind. Variolite 
has also been found in the Point-Bonita rock.” 
(iii). The limestones have been described by Dr. Callaway, 
Prof. Bonney, the Rev. J. F. Blake, and others,’ and no further 
petrological details are needed for the purpose of this paper. 
(iv). The grits are of importance, chiefly in connection with the 
question of the age of the rocks ; and a detailed description is not 
necessary here. They are moderate to very fine in grain, the finer 
beds passing gradually into shale. Bedding is seen in many places, 
and very clearly in the Newborough district, where it is rapidly 
1 Cole & Gregory, Quart. Journ. Geol. Soe. vol. xlvi (1890) p. 295. 
2 Ransome, Bull. Departm. Geol. Univ. Calif. vol. i (1893) p. 99. The 
yariolites of the Lleyn, described by Miss Raisin in Quart. Journ. Geol. Soc. 
yol. xlix (1893) p. 145, belong, no doubt, to the same series as those of Anglesey. 
3 Quart. Journ. Geol. Soc. vol. xxxvii (1881) p. 236; Brit. Assoc. Rep. 1888 
(Bath Meetg.) p. 389. 
