156 Geological Society : — 



Prague, induced the author to obtain some further particulars re- 

 garding the older rocks of Bavaria and Bohemia ; and a large part of 

 this communication referred to the sketch map and section supplied 

 to him by that gentleman. 



One of Sir Roderick's principal objects in exploring this region 

 was to convince himself, if possible, of the existence of a fundamental 

 gneiss of as high antiquity as the Laurentian rocks of Canada and 

 Scotland, and of the truth of M. Giimbel's view of the distinction of 

 the gneiss into older and younger ; but, after a survey of the whole 

 district, he was unable to distinguish any order of superposition 

 between its two members, the so-called younger gneiss, in one ex- 

 tensive tract near the Danube, dipping, according to M. Giimbel, 

 under the older ; and their variable strike rendered it as difficult to 

 judge by that character as by their dip, its direction in some places 

 being at right angles to what it is in others. For the present, 

 therefore, though with the greatest respect for the labours of 

 M. Giimbel, he considers the gneiss-rocks to constitute one great 

 series, it being certain that the two varieties are not separated by 

 any different intervening sediment, as in the N.W. of Scotland. 



A clear illustration of the whole ascending succession is afforded 

 by the order of superposition exhibited in M. Giimbel's section from 

 Hof to Selb, a distance of about seven or eight miles. Gneiss is 

 there seen resting against granite, and passing up into mica-slate 

 underlying concretionary, quartzose, chloritic masses, which form the 

 base of the Urlhonschiefer. This primary clay-slate is followed by 

 quartzites and black roofing-slate, in the latter of which the fossils of 

 the Silurian Primordial Zone of Barrande occur, and ultimately by 

 other Silurian, Devonian, and Lower Carboniferous strata in conform- 

 able succession, the latter passing conformably upwards into Mountain 

 Limestone, which is shown to be quite unconformable to the Upper 

 Carboniferous of Germany. In the remaining north-west portion of 

 the section the strata are repeated in inverted succession, having 

 been dislocated by the intrusion of igneous rocks. 



Sir Roderick next adverted to the question of the parallelism of 

 the Silurian Rocks of Bohemia with those of Britain, pointing out 

 that the Austrian Geological Survey, whose new map he exhi- 

 bited, had adopted, for this occasion only, the colours used by the 

 Geological Survey of Great Britain ; and he stated his belief that too 

 close a parallelism between the subformations had been attempted, 

 and that the parallelism of such large groups only as Lower and 

 Upper Silurian, as proposed by Barrande, with a possible interpo- 

 lation of "Middle Silurian," could be maintained. 



The author then contrasted the absence of Devonian and Lower 

 Carboniferous Rocks, coupled with the full development of Lower 

 and Upper Silurian life, in Bohemia with the fuller and unbroken 

 succession in Bavaria. He concluded by observing that the 

 conformable succession of strata in Bavaria and other tracts shows 

 the existence of beds which bridge over the gaps, represented 

 by unconformities, that occur in the British series ; and pointedly 

 adverted to the two facts, that the enormous thickness of clay-slate 

 beneath the Primordial Zone, though unaltered over large areas, 



