10 L. H. Borgström. (LVII 



At still active volcauoes this zoiie may iiearly coiiicide with 

 the surface itself. — As the teiision of the watervapour at 

 320° is about 110 atmospheres, the pressure of a watercolumn 

 1,000 m high woiild suffice to keep the water condensed at 

 the highest temperature, which is possible inside the region, 

 in which the arsenicsulphides may occur. On this account 

 it is very probable that the water, which at greater depths 

 than 1,000 m may have eiitered the fissures etc, in which 

 these minerals occurred, has been iii the fluid state. Only 

 in the uppermost part of the crust a slightly superheated 

 steam may have been in contact with realgar and auri- 

 pigment without causing them to fuse, — It is very inter- 

 esting to compare the geological evidence of the occurrence 

 of arsenicsnlphides with these data. The genetic conditions 

 are obvious in such places, where these minerals occur among 

 the sublimationproducts formed by the heat from burning 

 coalseams as near Dresden and in several localities in the Pla- 

 teau Central in France, in which realgar and auripigment 

 have been found with snlphur and salmiac, or at such places, 

 where these minerals have been produced a t the accidental 

 burning of orepiles consisting chieily of pyrite, marcasite and 

 blende, as at Beuthen in Silesia. The occurrences, where the 

 minerals in question are volcanic sublimationproducts, as at 

 Vesuvius, Volcano and Etna, form a different genetic group. 

 A near relation to this group bear the deposits containing 

 realgar or auripigment, which are separated from the water 

 of hot springs, for instance in Yellowstone National Park and 

 near Pereta in Tuscany. From this last kind of deposit, 

 there are transitional stages to the important genetic group, 

 to which all those localities belong, in which the arsenic 

 minerals appear with stibnite in veins rich in gold and 

 silver and connected with young (tertiery) dacite and andesite 

 surface-eruptives, as for instance at the famous mines of 

 Nagybanya, Felsöbanya, Kapnik and Nagyag in Hungary. 

 Also these deposits are formed near the surface. Likewise 

 are all secondary realgar and auripigment produced in the 

 neighbourhood of the outcrops of ore deposits clearly formed 

 at a low temperature and at an inconsiderable depth below 



