1866.] GUMBEL — ON LAURENTIAN ROCKS. 87 



way I soon convinced myself of the general similarity of our 

 organic remains with those of Canada. Our examinations were 

 made on polished sections and in portions etched with dilute nitric 

 acid, or, better, with warm acetic acid. The most beautiful 

 results were however obtained by etching moderately thin sections, 

 so that the specimens may be examined at will either by reflected 

 or by transmitted light. 



The specimens in which I first detected Eozoon came from a 

 quarry at Steinhag, near Obernzell on the Danube, not far from 

 Passau. The crystalline limestone here forms a mass from fifty 

 to seventy feet thick, divided into several beds, included in the 

 gneiss, whose general strike in this region is N.W., with a dip of 

 40°-60° N.E. The limestone strata of Steinhag have a dip of 

 45° N.E. The gneiss of this vicinity is chiefly grey, and very 

 silicious, containing dichroite, and of the variety known as 

 dichroite-gneiss ; and I conceive it to belong, like the gneiss of 

 Bodenmais and Arber, to that younger division of the primitive 

 gneiss system which I have designated as the Hercynian gneiss 

 formation ; which both to the north, between Tischenreuth and 

 Mahring. and to the south, on the south-west of the mountains 

 of Ossa, is immediately overlaid by the mica-slate formation. 

 Lithologically, this newer division of the gneiss is characterized by 

 the predominance of a grey variety, rich in quartz, with black 

 magnesian-mica and orthoclase, besides which a small quantity of 

 oligoclase is never wanting. A farther characteristic of this 

 Hercynian gneiss is the frequent intercalation of beds of rocks 

 rich in hornblende, such as hornblende-schist, amphibolite, diorite, 

 syenite, and syenitic granite, and also of serpentine and granulite. 

 Beds of granular limestone, or of calcareous schists are also never 

 altogether wanting ; while iron pyrites, and graphite, in lenticular 

 masses, or in local beds conformable to the great mass of the gneiss 

 strata, are very generally present. 



The Hercynian gneiss strata on the shores of the Danube near 

 Passau are separated from the typical Hercynian gneiss districts 

 which occur to the north, on the borders of the Fichtelgebirge and 

 near Bodenmais and Arber, by an extensive tract, partly occupied 

 by intrusive granites, and partly by another variety of gneiss. 

 These Danubian gneiss strata are not seen to come in contact 

 with any newer crystalline formation, but towards the south are 

 concealed by the tertiary strata of the Danubian plain ; while 

 towards the N.W. they are in part cut off by granite, and in part 



