240 



Proceedings of the Royal Physical Society. 



Zn., Pb,, Mn., Ni,, & Co. not determined. 



Jurassic. — (4.) At Harzburg four beds of fossiliferous 

 oolitic brown ironstone (FcgOg HgO) occur in the Ammonites 

 Bucklandi beds of the Lower Lias, which is here inverted at 

 an angle of 60°. They have an aggregate thickness of ISJ 

 feet, and are mined for the ironworks of Harzburg. 



h. Subsequent Deposits. 



A. In massive rocks. (1.) At Zorge there are veins of 

 haematite in the diabase which rarely pass out into the sur- 

 rounding Kieselschiefer and greywacke. The ore is accompa- 

 nied by quartz, brownspar, calcspar, etc., and is evidently 

 derived from the surrounding rocks out of which the iron 

 has been partially dissolved and redeposited in the fissures. 



(2.) The Permian porphyrites of Ilfeld are traversed by 

 small veins of Manganese ores — Manganite (MngOg + HgO), 

 Pyrolusite (MnOg), Varvicite (Mn^Oy + HgO), Braunite 

 (MugOg), Hausmannite (MugOJ, Psilomelan and Wad. 

 These are accompanied by barytes, calcite, brownspar 

 (Ca. Mg. Fe.) CO3, and occasionally manganese spar (MnCOg). 

 On passing downwards the veins become poor, and usually 

 disappear at a depth of 5 or 6 fathoms. 



B. In stratified rocks.^ — (3). The great ore deposits of the 

 Harz are the veins of Clausthal and St Andreasberg which 

 have been mined for the last six centuries. The Clausthal 



^ Seen on section No. 1. 



2 9iKilo. N.N.E. of Ernst. 



* The Clausthal veins are described in detail by von Groddeck in ** Zeit. 

 d. d. geol. Ges.," vol. xviii., 1866, pp. 693-776 ; and xxix., 1877, p. 440 ; 

 and those of St Andreasberg by H. Credner, vol. xvii., 1865, pp. 163-231. 



