358 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Apr. 22, 



Thus, on the eastern flank of the Silurian basin of Prague, M. 

 Giimbel's younger member of the gneiss, after conforming, with a 

 north-easterly strike, to the superjacent clay-slate and Silurian rocks, 

 folds round by devious bends until it reaches the southern end of 

 the mountainous wooded region called the Bohmerwaldgebirge. 

 There, where the gneiss-rocks are associated with vast masses of 

 granite, the longer axes of which are directed from W.S.W. to 

 E.N.E., both the older and younger gneiss have a coincident strike, 

 and they both range at a right angle to the dominant direction of 

 the strata in those parts of the region where they flank the fossiii- 

 ferous Silurian rocks. 



I examined in some detail the gneiss-strata on the banks of the 

 Danube, between Linz and Passau, which form the southern fringe 

 of the Bohmerwaldgebirge; and, judging from their strike, which 

 diverged from that of all those beds of gneiss with which I was 

 acquainted to the S.E. of Prague, I thought that they might repre- 

 sent the older gneiss. Again, judging from their very siliceous 

 character, and led by the analogy of their structure and their having 

 the same direction as the older gneiss of the West Highlands of 

 Scotland, I at first inferred that they were probably inferior to other 

 gneiss-rocks lying to the N.E., as well as to those near Purth. 



In these rocks of the Danube, whether at Passau or Linz, I saw no 

 trace of micaceous schists or serpentines, or any of those associations 

 which M. Giimbel assigns to the upper gneiss. On the contrary, I 

 found the grey gneiss, particularly at Linz, to be so eminently quartz - 

 ose and siliceous, that the fine white layers of quartz and felspar con- 

 stituted the dominant feature, as contrasted with the dark layers of 

 black mica. Such opinions, however, were necessarily modified by 

 the information kindly offered to me by M. Giimbel, and as laid down 

 in his little sketch-map. Thus, to the N.W. of Cham, the older 

 gneiss of that author, first ranging to the N.W., then bends to the 

 N.E., and is followed by the younger gneiss. The latter, folding 

 round large masses of granite, after several contortions, passes away 

 with a normal north-easterly strike, as it extends to the south of 

 Marienbad and Karlsbad. 



Again, as M. Giimbel shows in his map, the gneiss which he 

 believes to be the younger is that which ranges by Passau, and 

 occupies the gorges of the Danube — the very rock which I had sup- 

 posed to be of older date. Now, as he marks these, his younger 

 rocks, as dipping to the N.E., so as to seem to pass under his newer 

 beds, he was naturally struck with the anomaly. He supposes, 

 indeed, that this anomaly may be accounted for by a grand inversion 

 similar to the numerous cases of overthrow in the Alps, which he, as 

 well as others, has described. But, from what I saw, I cannot as 

 yet coincide with him in this view, inasmuch as the grand buttresses 

 of gneiss and granite which occupy the banks of the Danube between 

 Passau and Linz, and which are presumed by him to be the younger 

 gneiss, occupy a very low country, with no mountain-chain nor 

 igneous rock to the S.E. or at the back of them, by which we might 

 account for their upheaval, and yet they all incline rapidly to the N. 



