PROCEEDINGS OE GEOLOGICAL SOCIETIES. 



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in bands ; a casting of part of an ornament, exhibiting its perfect recon- 

 version to the Eowley Eag ; a specimen broken from a large mass of the 

 recrystallized basalt ; specimen resembling a natural vesiculated lava 

 (when fused the Eowley Eag 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 which 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 workman 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 refilled three or 

 four times) ; polished specimens of Mr. Chance's rolling of the obsidian glass 

 from -g- of an inch to f thick, 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 \ 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 

 had had frequent opportunities of examining streams of lava which showed 

 all the varieties of texture from compact basalt to those of obsidian and 

 pumice. What he had seen made him quite agree with the views expressed 

 in Mr. Plant's paper. In the neighbourhood of a volcano might be seen 

 rocks of considerable thickness w r hich 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 Eag, being hard 

 and of a sub-crystalline texture. It appeared quite clear that parts of the 

 same mass of lava became: 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 w T ater 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 

 with success. At the same time it was not yet considered that the success 



