114 OBSERVATIONS ON BASALT, &X. 



tenacious, from which a large ladle-full was taken, which, on 

 being allowed to cool, retained the characters of perfect glaf;. 

 The fire was maintained, though with gradual diminution, for 

 more than fix hours; after which time, the draught of the 

 chimney was intercepted, the furface of the glafs was covered 

 with healed fand, and the furnace was filled with coals, which 



Slow congela- were confumed very flowly. It was eight days before the 

 mafs in the furnace was fufficiently cool to be extracted, and 

 even then it retained confiderable internal heat. 



Appearance of The form of the mafs, being given by the bottom of the 

 furnace, was confiderably irregular, approaching to the fhape 

 of a wedge whofe lower angles were rounded. It was nearly 

 three feet and a half long, two feet and a half wide, about four 

 inches thick atone end, and above eighteen inches at the other. 

 From this diverfity of thicknefs, and from the unequal action 

 of the heat of the furnace, too great an irregularity had pre- 

 vailed in the refrigeration of the glafs, to permit its attainment 

 of a homogeneous texture. Thefe circumstances might proba- 

 bly have been counteracted by better devifed precautions; but 

 the inequality of the product is not to be regretted, fince it has 

 fortuitously difclofed fome very lingular peculiarities, in the 

 arrangement of bodies paffing from a vitreous to a ftony irate, 

 which might have remained unobferved, if the defired homo- 

 geneity of the refult had been obtained. I (hall now endeavour 

 to defcribe the various products of fhis operation ; and I thai! 

 alfo fubmit to your confideration, fome remarks which appear 

 to me to arife naturally from the phenomena I have obferved ; 

 premifing that, except where my opinions are fupported by 

 the unequivocal demonstration of facts, I offer them with the 

 utmoft deference to the decifion of more experienced and 

 judicious mineralogies and geologifh. 



External charac- * l ma y ^ e P r0 P er t0 g ive a concife description of rowley rag 



rers, &c. of itfelf before I confider the products which it yields by igneous 

 owley iag. fa fion. This fpecies of bafalt is fine-grained, of a confufed 

 cryftallized texture ; its fracture uneven in fmall pieces, con- 

 choidal in large pieces. Its hardnefs fuperior to common glafs 

 but inferior to feldfpar. Its tenacity confiderable. Its action 

 on the magnetic needle firong, but without figns of polarity* 

 Its fpecific gravity, according to my trials, 2.868. Its general 

 colour iron gray, approaching to black. It is opaque ; and it 

 4 reflect 



