Vol. 58.] THE JASPERS OF SOUTH-EASTERN ANGLESEY. 429 
composed of ellipsoidal or spheroidal masses, piled and pressed upon 
one another, as if they had been rolled over and over in a semi- 
consolidated condition (figs. 2 & 3, p.428). Sometimes between the 
masses are small interspaces; sometimes smaller ellipsoidal or pillowy 
masses fit into gentle re-entering curves in the sides of larger ones, 
suggesting very vividly, hard though they now are, the rolling and 
pressing against each other of pasty, yet individualized bodies.’ 
A graphic description of their aspect will be found in the Rev. J. F. 
Blake’s ‘ Monian System’? This structure is here dwelt upon, on 
account of its close resemblance to, in fact identity with, the ‘ pillowy’ 
structure of the basic lavas of the South of Scotland and other 
localities. Figs. 2 & 3 will at once recall the frontispiece in the 
Geological Survey Memoir on that district,’ and also the rocks of 
Mullion Island at the Lizard, and Point Bonita in California.* 
The pillowy masses are of two types—a larger and a smaller; and 
though they occur together, yet one or the other usually predominates 
’ inany onesection. The larger (about 4 feet long) is ellipsoidal, the 
smaller being, as arule, more nearly spherical. The middle axis of 
the ellipsoid is generally vertical, and the longest lies north-east and 
south-west: the ellipsoidal ‘pillows’ therefore stand ‘on edge.’ No 
marked difference of crystalline texture has been observed between 
the inner and outer parts of the ‘ pillows,’ but a concentric shell- 
structure is common, which becomes sometimes almost a concentric 
fissility. Small spherical amygdules are not uncommon, but they 
are not a marked feature of the rocks. The general microscopic 
character agrees with that of the Scottish and other pillowy rocks. 
This pillowy structure is seen at Tan y Graig in the Pentraeth area ; 
but it is much better displayed among the Newborough sand-hills, 
where the great bosses of volcanic-lcoking, dark-green rock, rising 
from beneath great drifts of sand, have a most singular, and some- 
what forbidding aspect; and as they are, besides, kept bare of vege- 
tation by the incessant sweep of the sand-blast, the whole aspect 
of the scenery has a desert-like look that one does not expect to 
see in Britain. 
It is in these pillowy diabases that the variolite first observed 
by the Rev. J. F. Blake,’ and afterwards described by Prof. Grenville 
Cole,° occurs. Prof. Cole has moreover been so kind as to write for 
me the following description of a variolite which occurs in the pillowy 
rock of Tan y Graig, Pentraeth :— 
‘No. 5, 1899.—The large spherulite from which this is cut clearly enveloped 
a previously banded and spherulitic mass, just as the large spherulites in acid 
? Rocks of this kind have been referred to as ‘spheroidal,’ but the structure 
is evidently distinct from ordinary spheroidal jointing produced after consoli- 
dation: see Platania, ‘Geology of Acireale’ in Dr. Johnston-Lavis’s ‘ South 
Italian Voleanoes’ 1891, pp. 41-43. 
* Quart. Journ. Geol. Soc. vol. xliv (1888) pp. 510-11. 
* *Silur. Rocks of Britain’ vol. i (1899) pl. i. 
* Trans. Roy. Geol. Soc. Cornwall, vol. xi (1893) p. 565; ‘Eruptive Rocks 
of Pt. Bonita’ Bull. Departm. Geol. Univ. Calif. vol. i (1898) pl. vii, p. 78. 
° * Older Rocks of Anglesey’ Brit. Assoc. Rep. 1888 (Bath Meetg.) p. 416. 
© Sci. Proc. Roy. Dublin Soe. n. s. vol. vii (1891) p. 112. 
