308 PROCEEDINGS OF PROVINCIAL SOCIETIEff. 



ing to black ; as opaque, but reflecting light from numerous brilli- 

 ant points and facets of hornblende and feldspar. Dr. Kennedy 

 says it is composed of silica 48, alumina 16, lime 9, soda 4, oxide of 

 iron 16, mur. acid 1, water 5. 



Of this substance 3 1 cwts. were melted in a reverberatory furnace, 

 heated to the usual degree for puddling iron, in 4| hours ; and 

 every precaution was taken to ensure the slow cooling of the mass, 

 by filling the furnace with fuel, and closing every aperture. At the 

 end of a fortnight, the fuel was all consumed, and, the furnace hav- 

 ing been taken down, the basalt was found in a solid mass, still too 

 hot to hold, above 5 feet long, 4 feet wide, and 1 8 inches thick. 



Upon breaking it, the following were the appearances presented : 

 an upper stratum of vesicular stony matter, about an inch in thick- 

 ness ; evidently the production of the ebullition of the liquid mat- 

 ter, caused by the escape of its gaseous constituents from the action 

 of the heat. Next, a layer of black glass, from two to eight inches 

 thick, on the side of the mass that was exposed to the air from the 

 doors of the furnace ; elsewhere, immediately under the vesicular 

 covering, the solid stone occurred, interspersed, however, here and 

 there, with air bubbles, but otherwise very little different from the 

 structure of the basalt before it had been submitted to the fire ; 

 possessing the same crystalline appearance, but distributed in a 

 more regular manner, for, in most instances, the crystals and facets 

 seemed to radiate from central spots. 



As the quantity of basalt melted was greater than has ever been 

 before experimented on, and as the slow cooling of the bulk was 

 ensured by the gradual consumption of the supply of fuel, it was 

 hoped that something analogous to, if not resembling, the columnar 

 structure, might be discovered, upon breaking the mass. But al- 

 though this expectation was frustrated, yet several varieties of 

 structure were observed intermediate to the black glass and the per- 

 fect stone, which the writer considered worthy of being pointed out 

 to the society, particularly as they differed, in some degree, from 

 the results obtained by Mr. Gregory Watt from a similar experi- 

 ment. 



From the experiment of melting basalt, originally made by Sir 

 James Hall, and repeated by Mr. Watt, Dr. Corrie, and Dr. Ward, 

 it is certain that basalt melted and cooled quickly always becomes a 

 black glass ; and that its return from the vitreous to the stony state 

 depends entirely upon the rate of its cooling. The melting point of 

 basalt is about 38°, Wedgewood ; and if it be suddenly lowered from 

 this degree to 21° it becomes a black glass; but if gradually low- 

 ered to 28° it then begins to #rystallize, and becomes stony, and 

 this stony structure is the more perfect the longer the mass is kept 

 at the same temperature, and the more gradually it passes through 

 the intermediate degrees between 28 and 21. The same rule holds 

 in an increasing as well as in a decreasing temperature : thus, the 

 glass heated to 21°, and raised slowly to 28°, assumes the crystalline 

 state, but not if the heat be augmented rapidly. It is remarka- 



