35 



the north of Africa, to the most northern parts of Europe ; there- 

 fore the crystalline crust of the earth does not consist of confused 

 shapeless masses, resulting from igneous eruptions, but possesses 

 a structure and arrangement of parts as regular and uniform as 

 any other natural production. It has but one general grain, by 

 which any of the masses will split, and that is from pole to pole, 

 as represented in Plates IV. and V. This meridional grain is pro- 

 duced by the polar arrangement of the crystals in the granitic 

 base causing more or less vertical sheets or plates of mica, talc, 

 chlorite, &c, the influence of which, together with the constant 

 circulation of the polar currents in the direction of the planes, 

 extends to the sedimentary beds, and thus the whole of the sur- 

 face becomes uniformly cleaved. 



CHAPTER VI. 



ON THE GENERAL CHARACTER OF THE CRYSTALLINE ROCKS 

 CALLED " PRIMARY." 



The first remarkable fact that presents itself to our notice on 

 examining the nature of these rocks is, that they contain a 

 very considerable proportion of water, and are often found in 

 depth as soft as clay. Nothing is more common than springs, a 

 great number of which are daily forming incrustations of mi- 

 neral matter by precipitation, In New Granada great streams 

 of siliceous and calcareous matter are seen issuing out of the 

 rocks and forming large deposits. When the calcareous solvent 

 happens to predominate, the silica becomes aggregated into small 

 lumps, like flints in chalk, and when equal they form distinct 

 beds. In mines and caverns mineral springs are very abundant, 

 and numerous crystals are constantly forming, according to the 

 strength of the mineral solvents. A crystal thus produced may 

 with propriety be called " primary ," as it is formed from a pri- 

 mary element, like a crystal of salt from the sea, into a definite 

 form, according to exact laws ; and the powder of such a crystal 

 reconsolidated by any cement may be called a " secondary " or 

 cc sedimentary " formation. Therefore the terms " primary " and 



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