64 



OUTLINES OF GEOLOGY, 



In the upper strata of this formation the slatey rocks pre- 

 dominate, and in the lower gneiss ; the others occur in no 

 determinate order. 



152. No single stratum of the lower rocks of this order, 

 has ever been pursued to any great distance, nor do they 

 occur, as in the higher orders, in any determinate manner. 

 It may hence be surmised, that so far from each stratum be- 

 ing coextensive in formation, it has a form that may be 

 likened to flat plates, which, however extended, finally run 

 out. 



The stratification of this order is not only wanting in re* 

 gularity of succession in different places, but is more fre- 

 quently contorted and twisted from its original position than 

 any other. In some cases a section of the rocks exhibits 

 the joints in waving or even zigzag lines. This disturbance 

 extends so far that the order of the series appears inverted, 

 the rocks having been raised beyond the vertical position, 

 and, as it were, overturned. 



153. These disturbances may be explained by reference 

 to the action which has penetrated the whole order by innu- 

 merable veins, which are often the seat of valuable ores. 

 Metallic minerals are also disseminated. Among those found 

 in either mode are : 



Magnetic iron ; Galena ; 



Specular iron; Argentiferous Galena; 



Iron pyrites ; Blende ; 



Arsenical pyrites ; Chromate of iron ; 



Copper pyrites ; Gray cobalt : 



Sulphuret of copper; Sphene; 

 Native copper ; Titaniferous iron ; 



Native gold ; Columbium ; 



Molybdena ; Oxide of tin. 



Anthracite is found in the clay slate, and graphite in the 

 lower rocks. 



