80 A DESCRIPTION OF THE [Ch. V. 



in primitive clay-slate. Small crystals of hornblende not un- 

 frequently also appear, but no quartz, except in isolated and 

 rare beds. Nearer the valley of the Nid, however, the mica 

 appears continuous and shining, in the manner of mica-slate, 

 but always fine and straight, slaty, and without quartz, which 

 we should rather expect to be the case in clay-slate. At 

 Kiistad, about two miles from Drontheim, the rocks occur in 

 other forms. The mica can no longer be mistaken : its folia 

 surround a kernel, and form large balls of two and three feet in 

 diameter. The kernel is extremely compact and hard, fine 

 splintery or fine granular in the fracture, and of a bluish 

 grey colour. It is probably a mixture of much compact fel- 

 spar, a little quartz, and fine mica folia. The surrounding 

 mica is also bluish-grey, glistening, and continuous, and 

 every where covered with a multitude of beautiful pinchbeck- 

 brown scales of mica. These balls lie close together, and 

 whole rocks consist of them. We are frequently tempted to 

 consider them as a conglomeration of large blocks ; but the 

 nature of the mica, and the position of this rock between 

 other strata of mica-slate, distinctly prove that it cannot be 

 separated from the mica-slate formation ; this indistinctness 

 of character and constant change in its ingredients show, 

 however, that the mica-slate approaches very nearly the tran- 

 sition into clay-slate.* 



The clay-slate, also, like mica-slate, often passes into mag- 

 nesian rocks : first, it becomes very fissile, soft, and unctuous 

 to the touch ; and then it is found to contain beds of a talcy 

 nature, resembling potstone, which is composed of fine 

 granular talc mixed with quartz, and its properties vary 

 according to the proportion of these minerals : sometimes it 

 is very fine grained and semi- hard, with splintery fracture, and 

 when talc prevails it is soft and sectile.f 



The composition and the geological relations of the rocks 

 of the island of Kielvig are very remarkable, and deserving 



* Travels through Norway and Lapland, p. 106. f Idem, p. 91. 



