1866.] GUMBEL — ON LAURENTIAN ROCKS. * 89 



such quantities that it is profitably extracted, and is largely used 

 for the manufacture of the famous Passau crucibles. In all of 

 the numerous graphite mines, the uniform interstratification of 

 bands and lenticular masses rich in graphite with the gneiss 

 is here distinctly marked. A similar .arrangement is seen in the 

 sulphurets of iron, which are more abundantly disseminated in the 

 more hornblendic strata. The localities of porcelain-earth or 

 kaolin are in like manner confined to the strike of the gneissic 

 strata ; and are generally contiguous to certain interstratified 

 granitic and syenitic bands, rich in feldspar. Its frequent 

 association with porcelain-spar, (probably nothing more than 

 a chloriferous scapolite or anorthite,) indicates that this mineral 

 has played an essential part in the production of the kaolin. The 

 presence of chlorine in this mineral is highly significant, and 

 suggests the agency of sea-water in its production. 



Of particular interest, from their mineral associations, are three 

 or more parallel bands of crystalline limestone of no great 

 thickness, which occur conformably interstratified with the gneiss 

 of the hills near Passau. They begin near Hofkirchen, and 

 extend north and south, from along the Danube as far as the 

 frontier, near Jochenstein, where the Danube leaves Bavaria. 

 These separate limestone bands, although exposed by numerous 

 quarries, cannot be followed uninterruptedly, being sometimes 

 concealed, and sometimes of insignificant thickness. 



The large quarry of Steinhag already described, from which I 

 first obtained the Eozoon, is one. The enclosing rock is a grey 

 hornblendic gneiss, which sometimes passes into a hornblende- 

 slate. The limestone is in many places overlaid by a bed of 

 hornblende-schist, sometimes five feet in thickness, which separates 

 it from the normal gneiss. In many localities, a bed of serpentine, 

 three or four feet thick, is interposed between the limestone and 

 the hornblende-schist ; and in some cases a zone, consisting chiefly 

 of scapolite, crystalline and almost compact, with an admixture 

 however of hornblende and chlorite. Below the serpentine band, 

 the crystalline limestone appears divided into distinct beds, and 

 encloses various accidental minerals, among which are reddish- 

 white mica, chlorite, hornblende, tremolite, chondrodite, rosellan, 

 garnet, and scapolite arranged in bands. In several places the 

 lime is mingled with serpentine, grains or portions of which, often 

 of the size of peas, are scattered through the limestone with 



