1866.] GUMBEL — ON LAURENTIAN ROCKS. 83 



far as these fossiliferous primary limestones are concerned, as an 

 established fact. 



So early as 1853, after investigating the primitive rocks of 

 eastern Bavaria, which are connected with those of the Bohemian 

 forest, I expressed the opinion that, although eruptive masses of 

 granite and similar rocks occur in that region, the gneiss was of 

 sedimentary origin, and divisible into several formations. I at 

 that time endeavored to separate these crystalline schists into 

 three great divisions, the phyllades, the mica-schists, and the 

 gneiss formation, of which the first was the youngest and the last 

 the oldest ; all these formations having essentially the same dip 

 and strike. 



These results, obtained from very detailed geological and topo- 

 graphical researches, were subsequently more fully set forth in the 

 Survey of the Geology of Eastern Bavaria, (Book IV., p. 219 et 

 seq.) ; where I endeavored to assign local names to the subdivisions 

 of the primitive rocks of that region. Beginning with the more 

 recent, I distinguished the following formations : 



1. Hercynian primitive clay-slate. 



2. Hercynian mica-slate. 



3. Hercynian gneiss. ) -r, . 



, -n .. . } Jrnniary gneiss system. 



4. Bojian gneiss. ) J ° J 



In some cases, within limited regions, I even succeeded in tracing 

 out still smaller subdivisions. It was in this way established that 

 definite and distinct kinds of rocks, as for example hornblende- 

 slate and mica-slate, may replace each other and, as it were, pass 

 into each other, in different parts of the same horizon. 



After Sir Roderick Murchison had established the existence of 

 the fundamental gneiss in Scotland, and recognized its identity 

 with that of the Laurentian system" of Canada, he turned his 

 attention to the primitive rocks of Bavaria and Bohemia. My 

 researches and my communications to him disclosed the important 

 fact that these rocks belong to the same series as the oldest 

 formations of Canada and of Scotland. On one point only was 

 there an apparent difference of opinion between Sir Roderick and 

 myself; which was that he was disposed to look upon the whole 

 of the gneiss of the Hercynian mountains as constituting but a 

 single formation, corresponding to the Laurentian gneiss of Canada 

 and of Scotland; while I had endeavored to distinguish two 

 divisions, the newer grey or Hercynian gneiss, and the older red 



