FORMATION OF PRIMITIVE MOUNTAINS. 



If primitive mountains and volcanic formations have 

 been fluid, and have crystallised on cooling, it is neces- 

 sary that we should retrace in them the same phenomena 

 and the same laws which we still observe at the present 

 time. If a fluid body become solid by cooling, these phe- 

 nomena are differently modified, according to the chemi- 

 cal nature of the bodies, and according to the crystalline 

 forms which they acquire on cooling ; but the laws remain 

 always the same. Mitscherlich says, I am in possession of 

 some specimens which explain several of the phenomena 

 so often shewn by basalt and volcanic formations. I do 

 not possess artificial basalt resembling the natural co- 

 lumnar kind ; yet the slags obtained at the furnaces of 

 Sahla resemble basalt so perfectly, as to deceive the most 

 experienced eye, especially as their cavities contain crys- 

 tals of augite. But I have found at Fahlun a bisilicate 

 of protoxide of iron, which has in consequence a com- 

 position analogous to that of basalt, and which has dis- 

 tinct joints. In this slag we perceive that the joints, 

 which are parallel to the axis of the prism and to the 

 lateral planes of the crystals, are always perpendicular 

 to the plane of cooling. This is particularly observable 

 in a specimen which was obtained by melting the slag in 

 a mould ; on crystallizing it had several planes of cool- 

 ing, and the joints are parallel to each of these planes. 

 The planes of separation in basalt present exactly the 

 same phenomenon as this slag. 



The phenomena which take place when a fluid body 

 crystallizes may be observed in sulphur, better than in 

 any other body. All fluid bodies, however, and even 

 water, on freezing, present the same phenomena. 



If a fluid body has cooled to the point at which it be- 



