1863.] MTTRCHISON BAVARIA AND BOHEMIA. 357 



will presently dilate upon these important contributions, which con- 

 stitute, in fact, a main part of this communication*. 



Gneiss of Bavaria and Bohemia. — One of my great objects in ex- 

 ploring this region was to satisfy myself, if possible, as to the 

 existence of a fundamental gneiss of as high antiquity as the Lau- 

 ren tian rocks of Canada, and those of the north-west Highlands 

 of Scotland, which I had described. For this purpose, besides 

 traversing the country from Marienbad to Pilsen, and thence to 

 Prague and Pardowitz on the east, I repassed from Pilsen by Furth 

 to Regensburg, and afterwards examined the huge masses of gneiss 

 and granite which form the southern wall of the chain of the 

 Bohmerwaldgebirge between Passau and Linz, on the banks of the 

 Danube. I was unable, in my partial examination, to satisfy my- 

 self that the true gneiss of any one part of this vast crystalline 

 region overlies another or more ancient gneiss. But M. Giimbel in 

 Bavaria, and M. Crejci in Bohemia, believe in the existence of an 

 older and a younger gneiss. As, however, I am not aware that an 

 order of superposition has anywhere been seen, I am the more dis- 

 posed to consider all the gneissose rocks which underlie the micaceous 

 schists and primary clay-slate as belonging to one great fundamental 

 group, though eventually these rocks may be separated by proofs 

 worked out by local observers. 



In order to convey to me his own ideas on this subject, M. Giimbel 

 has kindly transmitted to me a sketch-map (fig. 1) as condensed from 

 his long and laborious surveys, executed upon maps of a very large 

 scale. Dividing the gneiss into older and younger (2 and 3 of the 

 map), he distinguishes the first as a highly granitoid and reddish 

 rock, like the gneiss of the Erzgebirge, and containing 75 per cent, 

 of silex, and as being both intermixed with and penetrated by 

 granite. The younger or grey group of this gneiss contains courses 

 of hornblende, slaty greenstone, syenite, granulite, and serpentine. 

 The elder of these gneissose groups is roughly estimated by M. Giim- 

 bel to have a thickness of about 50,000 French feet, and the younger 

 group to be about 35,000 French feet thick; so that, as a whole, 

 the gneiss of Bavaria and Bohemia, according to this author, has a 

 maximum thickness of not less than 90,000 English feet ! 



Unable, as I have said, to see any order of superposition between 

 these two varieties of gneiss, I afterwards found that the same 

 variety of gneiss changed its direction so greatly in its range through 

 different tracts, that no inference respecting the age of the deposit 

 could be drawn from the strike of the strata. 



This is, indeed, clearly demonstrated by M. Giimbel's map (fig. 1), 

 by which it is seen that both the older and younger gneiss of that 

 author assume in some tracts the same strike, i. e. E.S.E. to W.N.W., 

 while in others they both change to a direction perpendicular or rect- 

 angular to the above, or from S.W. and W.S.W. to N.E. and E.N.E. 



* The detailed labours of M. Giimbel are not to be judged of by this little 

 sketch-map. He has, in fact, so closely examined the various rocks of granite 

 and gneiss and all the superjacent rocks, as to have laid them down on the huge 

 cadastral map of Bohemia which is called the " Fexier Cadaster." 

 VOL. XIX. r-ART i. 2 b 



