ON THE PKEDEVONIAN EOCKS GE BOHEMIA. 591 



42. On the Peedevonian Eocks of Bohemia. By J. E. Maee, Esq., 

 B.A., E.a.S.* (Read June 9, 1880.) 



Contents. ^ 



Page 



1. IntrodiJction 691 



2. Description of the Strata 692 



3. The Associated Igneous Rocks 598 



4. Comparison of the Strata with British Deposits 600 



5. Colonies 606 



6. Summary 617 



§ 1. Inteoduction. 



On examining tlie geological map of the neighlbourhood of Prague, 

 by Profs. Krejci and Helmhacker, it will be seen that the Predevonian 

 rocks are in many places covered by others of Cretaceous age. The 

 country in which they are developed is in fact a plateau formed by 

 a Postcretaceous plain of marine denudation, in which the rivers 

 have consequently not had much time to erode valleys ; the sections 

 of the Predevonian rocks are therefore principally found along the 

 sides of narrow valleys, wbich mostly run at right angles to the 

 strike of the beds. This strike, as may be seen in the above-men- 

 tioned map, or that of M. Barrande, is in a prevailing E.N.E. and 

 W.S.W. direction, and a system of faults runs parallel with it and 

 was produced at the same time. By consulting Prof. Krejci's ' Geology 

 of Bohemia' (printed in the Czech tongue), the sharpness of some of 

 the folds may be seen (c/. figs. 173, 180, &c.) ; in fact, although 

 the basin itself has a very simple structure, it contains some very 

 complicated foldings and repetitions in places. These may be weU 

 seen in the neighbourhood of Beroun, and are shown on Krejci's 

 map. These„ foldings, with the parallel faults, were produced in 

 Precarboniferous times, for Carboniferous rocks rest, nearly horizon- 

 tally, on the folded and faulted Cambrian, at Stradonice, near 

 Beroun, 



Another series of faults, however, affects the Predevonian rocks 

 and also the Carboniferous, and is hence Postcarboniferous, and this 

 series is approximately at right angles to the former. The folds 

 affect hard limestones and grits and soft shales alike ; and as the 

 rocks have been released from strain by crumpling and faulting, the 

 phenomenon of cleavage is of somewhat rare occurrence. The Pre- 

 cambrian rocks are slightly cleaved, but I have seen no true cleavage 

 in any of the Cambrian or Silurian rocks. This is a fortunate cir- 



* The author was sent out during the past year, by the University of Cam- 

 bridge, with a grant from the Wort's fund (Grace 2, Feb. 6th, 1879), to examine 

 and report upon the Cambrian and Silurian rocks of Bohemia, with special 

 reference to the boundary between them. In the following paper the results 

 obtained are laid before the Society. Professor Sedgwick's nomenclature is 

 adopted in this paper, and hence the term Silurian is hmited to the beds con- 

 taining Barrande's faunas E, F, G, and H. 



