DAVID FORBES — SOUTH COAST OF NORWAY. 2] 



the hornblende-schists occasionally, under such circumstances, as- 

 sumed the appearance of a dioritic rock. When, however, the 

 alteration was not so intense, the schists became felspathic for 

 some distance from the points of contact ; and thus hornblende- 

 schists became converted into hornblende-gneiss, mica-schists into 

 micaceous gneiss. Even when a granite-vein cut through the schists, 

 these became felspathic uear the points of contact, although other- 

 wise the beds themselves did not contain felspar. 



When granite broke through the quartzites and mica-schists, epidote 

 was generally developed ; if through hornblende-schist, mica and fel- 

 spar generally made their appearance near the points of contact. 



The eruptive rocks of this district are divided into two classes, 

 viz. acid and basic silicates. 



To the former class belonged three varieties of granite : — 



(«.) Granite consisting of oligoclase, quartz, and mica, and con- 

 taining, as accessory minerals, moroxite and sulphuret of molybde- 

 num, as at Skrubben, near Krageroe. 



(b.) Granitec omposed of orthoclase, mica, and quartz, as at Hest- 

 noesoerne, near Grimstad, and not known to contain other minerals. 



(c.) Granite which, when normal, contains two felspars (ortho- 

 clase and oligoclase), mica, and quartz, and is considered as younger 

 than the two preceding varieties, and probably more modern than 

 the Silurian beds, and also than the norite of the west coast. The 

 mineral orthite is particularly characteristic of this granite wherever 

 it makes its appearance ; and it is also remarkable for the presence 

 of minerals containing cerium, lanthanium, yttrium, &c. ; and even 

 many common minerals, otherwise not known to contain these ele- 

 ments, were found, on analysis, to contain them in considerable 

 amount when present in this granite, — as, for example, epidote, 

 apatite, titanite, garnet, scapolite, &c. Many rarer minerals also 

 occurred, as curenite, alvite, tyrite, ytterspath, &c. ; and these 

 minerals, though enclosed in the granite, generally contained a 

 considerable amount of water. 



This granite is very widely distributed from the western coast-line 

 of Norway to the Baltic ; and at Arendal the recent cuttings have 

 shown that over considerable areas the vertically-foliated gneiss is in 

 reality only a crust of comparatively few feet in thickness resting 

 upon this granite, as can be seen in a section of Helle Felspar Quarry 

 in a former Number of this Journal. 



To the basic silicates belong, — 



(#.) Diorite, consisting of a felspar with hornblende and titanite 

 of iron. It had not been previously noticed, although occurring very 

 largely in the district, and under very varied appearances — some- 

 times coarse-grained and in large mass, principally felspar with a 

 little hornblende — at other times a fine-grained rock, which is a 

 mixture of felspar, hornblende, and titanite of iron : when in veins it 

 generally consists principally of hornblende, with a little felspar 

 and titanite of iron. It forms the centre of many of the mountains 

 at Walbjerg, near Krageroe, and much alters the schists with 

 which it comes in contact. It contains, frequently, fragments of 



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