364 On the Paragenetlc Relations of Minerals. 



bear ore only to the depth of a few yards, corresponding to 

 the thickness of the cupreous slate, and the weissliegenden. 

 In the rothliegenden and in granite they terminate abruptly. 

 (This is likewise the case in the riicken of Sangerhausen 

 and Rothenburg, where rothnickelkies and nickel-glance pre- 

 dominate almost to the entire exclusion of spies cobalt.) In 

 the Riechelsdorf lodes pyrites containing nickel and cobalt 

 occur in the zechstein above the cupreous slate, although 

 near to it, and extend to a small distance beneath it. Traces 

 of bismuth have also been met with here. 



According to previous observation, gold and silver mine- 

 rals are altogether absent from this formation ; still the 

 fahlerz contains as much as J per cent, of silver, and although 

 this mineral, strictly speaking, does not belong to this group 

 of the formation which commences with heavy spar, as has 

 been shewn, it has been included because it appears in the 

 same lodes, and because it not unfrequently contains cobalt. 



As regards the great variety of minerals occurring in the 

 lodes, the Saalfeld district is the most important. 



It must be admitted that these five groups of the cobalt 

 nickel formation cannot be referred to one and the same 

 period, but must, perhaps, be separated into several lode 

 formations. The Chilian is undoubtedly distinct, and should 

 perhaps be placed immediately after the fifth formation. 

 Again, a group which includes lode quartz as an essential con- 

 stituent should, perhaps, be separated from one in which it is 

 absent. The want of observations respecting the relative age 

 of the individual lodes in which cobalt and nickel minerals 

 occur, the absence of spathic iron, and especially of barytite, 

 or their pseudomorphs, in some places have rendered it 

 necessary to consider under one head groups of minerals 

 which will, without doubt, hereafter be found to differ. 

 Still the course here adopted has the advantage of present- 

 ing a connected view of the known modes of occurrence of 

 bodies which in a mineral ogical, chemical, and geognostical 

 point of view are very closely related. 



Further, the localities enumerated admit of the conclusion 

 being drawn, that the most recent group belongs to a period 

 between the completion of the old coal formation, and but 



