Vol. 58. ] JASPERS OF SOUTH-EASTERN ANGLESEY. 431 
contorted. Cleavage, though general in the finer beds, is never 
very strong. The rocks are generally red or green, and full of 
volcanic débris: broken felspars, fragments of andesites and diabases 
and pink felsite, and lapilli blackened with iron-ores, being often 
abundant. Indeed they bear a strong resemblance to the ashy grits 
of Bangor; a fact which must be of the highest importance in 
considering their age and that of the Jaspers. 
(v). Cataclastic and schistose rocks. It is no part of 
the purpose of this paper to describe these rocks, the history of which 
belongs to that of the earth-movements and metamorphism which 
have affected the district ; but without some reference to them, no 
connected picture of the general field-relations of the jasper-bearing 
group as a whole could be presented. 
The least altered are breccias, generally more or less schistose. 
The more altered are for the most part dull greenish and reddish 
schists, the two being intimately connected. The Jaspers, limestones, 
and diabases are all found as fragments in the breccias, which are 
clearly cataclastic (‘ crush-conglomerate’). I have not, indeed, been 
able to satisfy myself of the pyroclastic origin of any rocks in the 
district, except two small bands among the pillowy diabases, and 
these appear to be true tuffs. The grits, too, can be seen in the act of 
breaking up into breccia. The rocks of the jasper-bearing group 
occur as lenticles in the dull. green schists, of all sizes, from the 
smallest discernible with a lens to masses a mile or two in length. 
In the Newborough district, original, and in the Pentraeth district, 
schistose matter appears to predominate: the undeformed masses 
float, so far as can be ascertained, in a schistose matrix, the whole 
forming a kind of gigantic crush-conglomerate. 
In the Beaumaris area the jaspers and limestones le among 
schists; but as an important metamorphic question comes in here, 
this district will only be touched upon in the latter part of the 
paper. 
II]. R&Etations AnD ORIGIN OF THE JASPERS. 
We may now deal with those relations of the jaspers to the diabases 
and limestones, especially to the diabases, the consideration of which 
is the principal purpose of this paper. 
The jaspers are found in the limestones ana diabases in innumerable 
lumps and seams, generally small. One or two are some yards long, 
but these are exceptional, and they are seldom more than a foot or 
two in any dimension. Many have no regular shape, but there is 
one mode of occurrence that is evidently original. This is when 
the interspaces between the ellipsoids and spheroids of the pillowy 
diabase are filled in with jasper (see fig. 3, p. 428). Where the 
pulowy structure is strongly developed, this is the typical mode of 
occurrence of the jasper, and it is admirably exposed in many of 
the great bosses of the Newborough sand-hills. 
