144 



LYELL'S ELEMENTS OF GEOLOGY. 



Alterations of Strata in contact with Granite. 



places for a distance of several hundred yards from the junction ; 

 and this black hornblende is so abundant, that eminent geologists, 

 when passing through the country, have confounded it with the 

 ancient hornblende-schist, subordinate to the great gneiss forma- 

 tion of Norway. Frequently, between the granite and the horn- 

 blendic slate, above mentioned, grains of mica and crystalline 

 felspar appear in the schist, so that rocks resembling gneiss and 

 mica-schist are produced. Fossils can rarely be detected in these 

 schists, and they are more completely effaced in proportion to 

 the more crystalline texture of the beds, and their vicinity to the 

 granite. In some places the siliceous matter of the schist be- 

 comes a granular quartz, and when hornblende and mica are 

 added, the altered rock loses its stratification, and passes into a 

 kind of granite. The limestone, which at points remote from 

 the granite is of an earthy texture, blue colour, and often abounds 

 in corals, becomes a white granular marble near the granite, 

 sometimes siliceous, the granular structure extending occasion- 



Fig. 126. 



Altered zone offossiliferous slate and limestone near 



Christiania. 



The arrows indicate the dip, and the straight lines the strike, of 

 the beds. 



ally upwards of 400 yards from the junction ; and the corals be- 

 ing for the most part obliterated, though sometimes preserved, 

 even in the white marble. Both the altered limestone and hard- 

 ened slate contain garnets in many places, also ores of iron, 

 lead, and copper, with some silver. These alterations occur 

 equally, whether the granite invades the strata in a line parallel 

 to the general strike of the fossiliferous beds, or in a line at right 

 angles to their strike, as will be seen by the accompanying ground 

 plan.* 



The indurated and ribboned schists above mentioned, bear a 



* Keilhau, Gcea Norvegica, pp. 61 63. 



