592 



STRATA IN CONTACT WITH GRANITE. [Ch, XXXV 



In the soutliera extremity of Norway there is a Large district, on the 

 west side of the fiord of Christiania, in which granite or syenite pro- 

 trudes in mountain masses through fossiliferous sti'ata, and usually sends 

 veins into them at the point of contact. The stratified rocks, replete with 

 shells and zoophytes, consist chiefly of shale, limestone, and some sand- 

 stone, and ail these are invariably altered near the granite for a dis- 

 tance of from 50 to 400 yards. The aluminous shales are hardened and 

 have become flinty. Sometimes they resemble jasper. Ribboned jasper 

 is produced by the hardening of alternate layers of green and chocolate- 

 colored schist, each stripe faithfully representing the original lines of strati- 

 fication. Nearer the granite the schist often contains crystals of horn- 

 blende, which are even met with in some places for a distance of several 

 hundred yards fi'om the junction ; and this black hornblende is so abun- 

 dant that eminent geologists, when passing through the country, have 

 confounded it with the ancient hornblende-schist, subordinate to the great 

 gneiss formation of Noi'way. Frequently, between the granite and the 

 hornblende 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 becomes 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 and blue color, and often abounds in 

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

 siliceous, the granular structure extending occasionally upwards of 400 

 yards from the junction ; the corals being for the most part obliterated, 

 though sometimes preserved, even in the white marble. Both the al- 



Fig. 705. 



' ' \ / ^^^ \ / nr anile, / ^ ^ > 



Altered zone of fossiliferous slate and limestone near granite. Christiania. 

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



tered limestone and hardened slate contain garnets in many places, 

 also ores of iron, lead, and copper, with some silver. These altera- 

 tions occur equally, Avhether the granite invades the strata in a line 

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



