Professor Bonney — Plant'Stems in Gneiss. 215 



side is iu contact with solid rock on the upthrow side, and it is 

 possible that the fault produces its full effect upon the solid floor. 

 However this may be, the fault coincides very closely with the 

 watershed in the valley. No water crosses it except a single 

 streamlet, and this rises only a yard or two away. 



Whatever the reason may be, therefore, we may safely say that 

 the valley north of Pant-gwyn lies in the trough between two 

 faults, and that this trough is closed at its southern end by 

 a transverse fault, which coincides with the watershed crossing 

 the valley ; and further, that many of the other faults apparently 

 produce on the surface of the ground an effect which is similar 

 in kind, if not in degree, to that which they produce on the strata 

 themselves. 



That these coincidences are accidental is, to say the least, 

 improbable ; and a simple explanation appears to be that the 

 valley was blocked out, so to speak, by the faults themselves, and 

 that the form so produced has been somewhat modified by subsequent 

 denudation. 



In advancing this view I am aware that it attributes to the faults 

 a more direct influence upon the topography than many geologists 

 will be disposed to allow. But although most valleys may have 

 been carved out by rivers, it is impossible to deny that some have 

 been formed by faults. 



It may be urged that since the formation of the faults there must 

 have been a vast amount of denudation which would obliterate their 

 effect upon the surface. But where erosion exceeds deposition, the 

 tendency of subaerial denudation is to accentuate rather than to 

 obliterate inequalities. Moreover, the evidence of the age of the 

 faults is extremely slight, and there is nothing to show that no 

 movement has taken place along them in comparatively recent 

 times.^ I shall show subsequently that, however the valley may 

 have been formed, it was probably not in existence when the 

 di'ainage system of the district was first established. 

 (jTo be concluded in our next Number.) 



III. — Plant-stems in the Guttannen Gneiss. 

 By Professor T. G. Boxxey, D.Sc, LL.D., F.R.S. 



AN important paper- on the reputed occurrence of fossil plant- 

 stems in gneiss of Carboniferous age at Guttannen, Switzerland, 

 by Messrs. E. v. Fellenberg & C Schmidt, for a copy of which 

 I am indebted to the courtesy of the authors, closes, if their view 

 be adopted, a comedy of errors. On this account a brief outline 

 of the story may be of service ; for it reduces this supposed relic 

 of Palaeozoic forests to a lusus natiirce, and, in any case, once more 

 illustrates the truth of the saying, " we are all fallible mortals." 



1 It may be uoted that Mr. C. Davison's researches on earthquakes in Great 

 Britain seem to indicate that even at the present time slips occasionally take place 

 along faults which are, in their origin, of very ancient date. 



2 £. V. Fellenberg & C. Schmidt, " Neuere Untersuchungen liber den sogen. 

 Stamra ira Gneisse von Guttannen" : Separat-Abdruck aus den Mitt, der Naturfors. 

 Gesell. in Bern, Jahrgang 1898. 



