PROCEEDINGS OF GEOLOGICAL SOCIETIES. 



353 



tinuation of the temperature speedily induced another change ; the texture 

 of the cooling material became more granular, its colour more grey, and 

 the brilliant points larger and more numerous. These brilliant molecules 

 arranged themselves in regular forms, and finally the whole mass became 

 pervaded with thin crystalline laminae. Mr. Watt applied these facts in 

 explanation of the globular structure which is observed in decomposing 

 basaltic rocks ; but as similar experiments have been often repeated, the 

 results are familiarly known to every geologist, and need not be further 

 alluded to in this paper. Sir James Hall, in 1805, conducted experiments 

 illustrating the crystalline arrangements and texture assumed by basaltic 

 rocks when fused and cooled under high pressure. He established the fact 

 that most rocks of presumed igneous origin, when fused, yielded different 

 products according to the differences in the amount of pressure under 

 which they were cooled. Thus, w r hen the rate of cooling was rapid, they 

 formed a black amorphous glass ; and when the cooling was slow, a strong 

 mass with a granular structure. The same materials yielded the most 

 dissimilar products, — a fact that is of the greatest importance in reference 

 to the study of the nature of eruptive rocks, and of the metamorphic action 

 which they occasion. These discoveries were chiefly valuable from their 

 philosophical bearing upon contested points in the science of geology ; and 

 it was not until the year 1846 that any attempt was made to turn them to 

 a practical and economical value. At that time, acting upon the results of 

 some experiments which had been made upon the Continent, a Mr. Jean 

 Michel Borgognon took out a patent in England for the manufacture of 

 articles of utility in what he termed artificial basaltic lavas. His inven- 

 tion claimed the discovery of operating upon stony substances, but chiefly 

 upon the vitreous slags from iron furnaces. These were fused at a high 

 temperature, and run into moulds of cast-iron or refractory clay, the 

 moulds being heated in the interior by means of a powerful flame, kept up 

 by a blast. Colouring matter, from the oxides of iron and other metals, 

 was mixed with the fused materials, and great diversity and beauty was 

 thereby obtained in the vitreous ornaments. It does not appear, however, 

 that any great application of his patented lavas was made in England. In 

 the year 1851 Mr. Henry Adcock, a civil engineer, of Oldbury, took out 

 the first patent for the production of bricks, tiles, pipes, etc., from the fused 

 trap of Rowley Regis. This gentleman had been led to the application of 

 this material from experiments which he had commenced in the year 1834. 

 He then fused some Rowley Bag in a common kitchen-fire ; and being much 

 impressed with the beauty of the black glass as it fell on the hearth, he 

 perceived that it might probably possess great practical value. He ob- 

 tained the use of a reverberating furnace, and conducted his experiments 

 upon a larger scale. In 1851 a patent w r as obtained, in which the inventor 

 claimed for his discovery the melting the stony material known as Basaltic 

 Trap, Rowdey Bag, or Whinstone, and running the same when in a fluid 

 state into moulds. The materials were heated in a reverberating furnace, 

 either at the bottom or in crucibles, and then cast into cast-iron moulds 

 put together with iron cramps. The fused trap was run into the moulds, 

 when both were brought into a state of white heat. If it were intended 

 to give a polished surface to the casting, the cast-iron mould was highly 

 polished and coated with plumbago, also highly polished. If the fused 

 materials were allowed to cool at a gradual and slow rate of cooling, the 

 result was a hard stony rock, scarcely to be distinguished from the original 

 trap from Rowley Regis ; but a less degree of heat, with a quicker rate of 

 cooling, caused the materials to assume the appearance of a mixed marble ; 



VOL. VI. 2 z 



