as illustrative of Geology. 81 



undergoing any other perceptible changes. Many phenomena 

 displayed by the changes that have ensued in the position of 

 the limestone strata, would not be explicable could we not as- 

 sume their softening by means of heat ; an assumption greatly 

 favoured by our experience. If in blast-furnaces the pressure 

 of the fluid masses eiFects the conservation of carbonic acid in 

 limestone, the same consequence ensued to the lime strata from 

 the great pressure of the sea. 



The heat of the melting furnace often produces in stones and 

 other masses contained in their centre, lasting changes, of a 

 perfect analogy to those displayed in mountain rocks, which, 

 by some means or other, have come in contact with masses to 

 which an igneous origin is ascribed. Clay-slate, which was used 

 for constructing a blast-furnace at Magdesprung, in the Anhalt 

 territory, had, from long operation of the heat, without having 

 become fluid, acquired an aspect like that of siliceous slate, an 

 appearance very much resembling the rock which is often found 

 in the neighbourhood of diabase, where this rock is in contact 

 with clay-slate. The changes have already been described (Got. 

 Gel. Anz. v. 1816, p. 490-493) which sandstones in the wall 

 of the pit or of the melting furnaces undergo from the heat. The 

 rocks pass into a more or less altered mass, by which the grains 

 disappear the more the farther the heating effect progresses. By 

 a smaller degree of the process the fracture appears dull ; by a 

 higher degree it assumes some lustre. The rocks become at the 

 same time rough and sonorous, often quite resembling the 

 quartz masses which are found in many districts ; for instance, 

 near Cassel and Dransfield, in the neighbourhood of basalt. The 

 sandstone usually loses the yellow or red colour, with which it 

 is originally invested ; a process apparently effected by the 

 transformation of the hydrate of the peroxide of iron, or the per- 

 oxide into the black oxide. In those places where the oxide of 

 iron was more accumulated in the beds of clay or marl that are 

 found in sandstone, there have arisen dark streaks or stripes of 

 a heated appearance, in consequence of a greater concentration 

 of the black oxide of iron. Besides these changes, there is not 

 unfrequently displayed in the building stones a division into 

 prisms, which we have already mentioned. This entire series of 

 phenomena is sometimes visible in strata of sandstone, in spots 



VOL. XXIV. NO. XLVIl. JANUARY 1838. F 



