THE TECHNOLOGIST. [June 1, 1864. 



496 ON GB'ANITE AND ITS USES. 



reducing them to its own likeness, and to the disintegrating influence of 

 water soaking into every pore, and dissolving ingredients essential to 

 their stability, till they are broken into pieces, worn into pebbles, 

 ground into sand, and degraded into mud. 



In this way tbe most ancient of the granite rocks of the world have, 

 in the remotest geological ages, utterly perished, and their relics, 

 strangely altered, are all that remain to us. Those relics, sifted and 

 sorted by the action of the waves, have afterwards been built up again 

 beneath the sea into coherent masses, have been consolidated by pres- 

 sure, have been hardened and, as it were, baked and semi-fused by sub- 

 terraneous fire, and, torn and twisted by volcanic forces, have been lifted 

 again to the surface, so as to form anew what we creatures of a day call 

 everlasting hills. 



Among those re-made rocks I notice, and that simply in passing, 

 that the mica of the granite is found predominating in certain of the 

 stones which can be split into roof-slabs and floor-slabs ; that the quartz 

 forms sandstones, such as we prefer in this city and neighbourhood for 

 building with ; and that the felspar changes into those clay-stones 

 which, when easily split, form our finest roofing-slates, and, when more 

 compact, our flagstones or pavements. 



Now, leaving unconsidered mica altogether, and passing without 

 further reference from the consideration of the slates and sandstones as 

 building materials, let us look at sand, i.e., ground-down quartz, as the 

 basis of glass ; and at clay, i.e., disintegrated felspar, as the chief consti- 

 tuent of pottery, and the source of the metal aluminium. Before doing 

 so, however, let me notice that certain even of the more recent granites 

 are so prematurely perishable, that they waste away even under serene 

 atmospheres, and crumble down so swiftly where other granites show no 

 signs of decay, that the continental geologists gravely refer to them as 

 " diseased granites." It is from them that our finest porcelain clay is 

 derived, so important an ingredient in pottery. First, however, of 

 glass. 



Pliny has a pleasant story of certain Phoenician sailors accidentally 

 discovering the mode of making glass, by kindling on a sandy river-bank 

 a fire to heat their cooking-vessels. These, for want of better supports, 

 were rested upon lumps of natron, that is, crystallised carbonate of soda, 

 such as is found at the present day in many parts of the world. The effect 

 of the fire, as the story goes, was to melt the sand and soda into glass. But 

 the story is incredible ; for natron, under a slight heat, dissolves in the 

 water which its crystals contain, and the fire must have been extin- 

 guished long before the sand and soda melted ; nor is it easy to under- 

 stand how an open fire could yield heat sufficient in any circumstances 

 to effect their fusion. But the legend, doubtless, is founded in truth. 

 Mankind probably first learned how to produce glass from striking inci- 

 dental phenomena unexpectedly brought under their notice. Among 

 such phenomena, special prominence may be assigned to the effect of 



