8 GEOLOGICAL MEMOIRS. 



clay-slate comes immediately upon the granite, without any trace of 

 the allochroitic formation, still less of the crystallized garnet, to be 

 observed. In such cases the hard slate is usually penetrated by the 

 granite. On its surface, when weathered, is seen an elaborate net- 

 work standing out ui relief, in which felspar is recognizable as a com- 

 ponent part. 



As we pass along the allochroitic beds b, b', we are sometimes 

 strongly reminded of gneiss. Numerous parallel lines of quartz, such 

 as are met with so abundantly in the old gneiss of Norway, traverse 

 it, and we almost forget that it is garnet and not mica and felspar 

 that lie between them. These allochroitic beds, bordering on the 

 granite, are also characterized by the following metallic minerals. 

 Magnetic iron, partly granular and crystalline, and partly developed 

 into distinct crystals (combinations of Rhombododecahedrons, Octa- 

 hedrons, and Hexahedrons) . Iron-pyrites. Copper-pyrites. Bismuth- 

 glance (this apparently occurs only near the Gjellebak mine). The 

 presence of copper-pyrites has led to mining operations here in 

 former times. 



Limestone, Clay-slate, and Granite to the South of Drammen. — 

 If we go from Gjellebak south-westwardly, along the main direction 

 of the strike of the limestone and clay-slate rocks, over the border of 

 the granite, down the Paradies-Bakken, and across the Lier and 

 Drammen Valleys, at a distance of about two miles we reach the 

 edge of the granite on the other side of the town of Drammen, and 

 there find another limestone and clay-slate area in contact with this 

 abnormal rock. On the whole there is a repetition here of the con- 

 ditions before noticed, partially, however, with their character still 

 more strongly marked. Granular crystalline limestone and allochro- 

 itic and otherwise altered clay-slate occur over a larger extent — an 

 area of transition rocks, about 2 miles long and ^ mile broad, being 

 enclosed on both sides by granite. But what still increases the de- 

 gree of metamorphosis, is the interpenetration of the clay-slate and 

 granite, observable in some mines here. The granite, therefore, in 

 this district had abundant opportunity of exercising its mighty in- 

 fluence ; nor has it failed to do so. Not only has it awakened, as it 

 were, the force of crystallization within the limestone and clay-slate, 

 but it appears also to have occasioned the formation of many mineral 

 veins along its borders. Of the minerals that thus owe their origiir 

 more or less directly to the granite, the following are particularly to 

 be enumerated. Magnetic iron in flat patches and in streaks within 

 the allochroitic zone. Garnet in extremely large quantities. Cop- 

 per-pyrites. Zinc-blende. Iron-pyrites. Lead-glance. Iron-glance*. 

 Cobalt-glance, sprinkled through a large flat band of magnetic iron. 

 Quartz. Calc-spar. Fluor-spar (nearly always in Octahedrons, not 



* This I find only in fragments of vein-ores on the rubbish-heap of one of the 

 Eckholt mines. These specimens consist of a breccia of hard clay-slate and which 

 exhibits the following characters. The individual clay-slate fragments were at first 

 slightly surrounded with iron-glance, or rather iron-glimmer (reminding one of 

 some Vesuvian phenomena). On this quartz crystals had been deposited, and the 

 remaining space was filled up with calc-spar and fluor-spar. 



