12 Sir James Hall on the Consolidation of the Strata. 



come to the assistance of some men just at the moment of 



need. 



Sir James concludes his Paper by adverting to some other 

 speculations which are not yet fully matured, but which he is 

 in hopes, ere long, to lay before the public. " A simple al- 

 lusion to one or two of these, 11 he says, " may perhaps be re- 

 ceived with indulgence. 11 



" I conceive, that salt, in the state of fumes, and urged by a powerful 

 heat, possibly also modified by pressure, or perhaps combined with other 

 substances, may have penetrated a great variety of rocks, acting as a 

 flux on some, as in basalt, granite, &c. ; agglutinating others, as in the case 

 of sandstone, pudding-stone, &c. ; softening others, as in the case of contort- 

 ed strata of greywacke. In many cases, too, 1 conceive that these fumes 

 may have had the power of carrying along with them various other mate- 

 rials, such as metals in a sublimed state, which would in this way be in- 

 troduced into rents, veins, and cavities, or may even have entered into the 

 solid mass of the rocks, which I imagine these fumes may have had power 

 to penetrate. I have already tried some experiments in pursuit of these 

 ideas. Salt, for instance, has been mixed with oxide of iron, reduced to 

 fine powder, and then exposed to heat along with quartzose sand. The 

 iron, I found, was borne up along with the salt fumes. The sandstone, 

 formed in this way, was deeply stained with iron, and other most curious 

 appearances presented themselves. 



" Every one who has seen a sandstone quarry, must have noticed evi- 

 dent traces of iron, the rock being stained in a great variety of ways ; 

 sometimes in parallel layers, — sometimes in concentric circles, or rather in 

 portions of concentric spheres, like the coats of an onion, — and, generally 

 speaking, disposed in a way not accountable by deposition from water. 

 All these appearances I would account for, by supposing the rock, either 

 at the moment of its agglutination into sandstone, or at some subsequent 

 period, to have been penetrated by the fumes of salt, charged with iron, 

 also in a state of vapour. 



" I may mention one very curious result of my experiments with salt 

 and iron, acting upon sand, namely, that, upon breaking up the specimen 

 of artificial sandstone, an appearance often presents itself of incipient cry- 

 stallisation, if I may use this term ; a number of large, shining, parallel 

 faces pervade the whole mass, and, by holding the specimen at the proper 

 angle to the light, this appearance becomes very obvious. What the na- 

 ture of these crystals is, I have not investigated ; but as they very much 

 resemble what we see in different kinds of sandstone, I am of opinion that 

 they hold out a fair expectation, of our being able to produce many of the 

 crystalline appearances with which we are familiar in nature. 



" Common sea-salt, such as I have used, as is well known, is not pure 

 muriate of soda ; and, in my experiments, I have mixed various other 



11 



