106 Scientific Proceedings, Royal Dublin Society.” 
Transverse or tangential cracks, the “fissures of retreat,” of 
Fonqué and Lévy, are of frequent occurrence in the varioles; in 
some cases they are traversed not only by the fibres of chloritized 
felspar, but by the opaque threads which we have regarded as 
representing decomposed glass (fig. 8). This adds a fresh difficulty 
in the way of their explanation ; it would appear that their forma- 
tion occurred while the glass was still viscid. Sometimes they are 
completely infilled with calcite, which in some cases has extended 
outwards from them in long prisms into the surrounding substance 
of the variole (fig. 9.) 
A chemical analysis was made of the variolitic rock from por- 
tions presenting a prevalent reddish colour, and another from 
portions mainly green. The following are the results :— 
Chemical Analysis of Variolite from Roundwood. 
Red variety. Green variety. 
S10,, : : 5 : 42°52 37°97 
Ti0,, ; : : ‘ *892 "92 
Al,0z, - < 5 5 18-10 19°45 
Fe,0s3, : : : ‘ 7°50 7°85 
FeO, : : : : 4°12 2°95 
CaO, ; : : : 6:07 18°25 
MgO, : ‘ : : 8°55 4°58 
K,0, 3 : : : 56 trace. 
Na,0, 5 ‘ é : 4°38 2°90 
H,0, : : A : 6°86 2°71 
CO,, ‘ ; : : trace 258 
99-50 100-16 
S]Op HNP ‘ : ; 2°94 3°01 
The water was determined by loss on ignition. A qualitative 
examination of the green variety showed the presence of a con- 
siderable quantity of manganese and chromium. The average 
specific gravity of the variolite is 3:05. 
It is scarcely probable that these analyses make any close 
approach to the original composition of the rock; and in our un- 
certainty as to the precise nature of many of the products of 
decomposition, particularly of the chloritic minerals and the white 
opaque granular material, we cannot attempt any calculation of its 
