PEOCEEDINGS OF GEOLOGICAL SOCIETIES. 
355 
in bands ; a casting of part of an ornament, exhibiting its perfect recon- 
version to the Kowley Eag ; a specimen broken from a large mass of the 
recrystallized basalt ; specimen resembling a natural vesiculated lava 
(when fused the Rowley Rag is very viscid, therefore, if a piece of wood, 
coal, or any other substance which will give off gas be plunged into 
it, the escaping gas will produce this vesiculated structure) ; specimens 
from the bottom of the furnace, in which the quartz gravel lining the fur- 
nace has become embedded in the melted lava (these are very similar to 
the toadstones and amygdaloid porphyries frequently met with in basaltic 
districts) ; a portion of the congealed coating which is instantaneously 
formed in the ladle used in pouring the melted matter into the mould 
(this is very similar to the crust va hich is observed on flowing lava from a 
volcano, and in a great measure preserves the under mass from cooling 
quickly ; it was turned to advantage in casting, as the fused basalt would 
remain for more than an hour in the ladle when thus coated, and experience 
taught the w orkman that fused metal so retained made castings of a supe- 
rior character; when a ladle was once coated to the thickness of half an 
inch it gained comparatively little in thickness, even when rehlled three or 
four times) ; polished specimens of Mr. Cliance's rolling of the obsidian glass 
from ^ of an inch to ^ thicL', used as a substitute for roofing slates, 
Bath tiles, and inlaid work for halls (these sheets were rolled 8 feet long 
by 3 feet 8 inches, and were readily cut into lengths with a glazier's dia- 
mond ; some were coloured by a mixture of glass ; one had a design 
engraved upon the polished surface by means of fluoric acid, showing its 
adaptability for this character of decoration ; one had a large percentage 
of glass and was coloured by a metallic oxide) ; artificial obsidian, cast in 
a cold iron mould ; another specimen cast in a heated iron mould ; part of 
an obsidian pipe, cast in a heated iron mould ; another pipe cast in a damp 
sand mould ; a hollow column, 6 feet high, 7 inches diameter (1 inch thick 
of this resisted a pressure of 300 tons ; a pipe 4 inches in the bore 
and I an inch thick resisted an hydraulic pressure of 220 pounds) ; artificial 
obsidian, with fine conchoidal fracture ; three specimens of artificial ob- 
sidian. 
Signor Berruti, of the Eoyal Geological Survey of Italy, said that in 
the course of his geological researches he had been in different volcanic 
districts where rocks occurred resembling the specimens on the table ; he 
liad had frequent opportunities of examining streams of lava which showed 
all the v^arieties of texture from compact basalt to those of obsidian and 
pumice. What he had seen made him quite agree with the views expressed 
in ^Ir. Plant's paper. In the neighbourhood of a volcano might be seen 
rocks of considerable thickness which at the top consisted of obsidian or 
volcanic glass, lower down the texture was of a duller and more earthy or 
stony character, and lower still, where the mass must have been a long 
time in cooling, it was very similar to basalt or Eowley Kag, being hard 
and of a sub-crystalline texture. It appeared quite clear that parts of the 
same mass of lava becam: a compact, stone-like basalt when cooled slowly, 
and other parts, when cooled rapidly, became obsidian ; for near Naples 
a stream of lava, which had flowed into the sea, was converted into obsi- 
dian where it had been immersed in the vrater and quickly cooled ; whereas, 
on the land, where the lava had cooled slowly, it had become more crystal- 
line and approximated in texture to basalt, — the material being evidently 
similar in both instances. In Italy an attempt had been made to turn it 
to some use, and to a certain extent the experiments had been attended 
\A ith success. At the same time it was not yet considered that the success 
