116 Prof. Hughes, [Mar. 9, 



think, reject the possibility of the scratched stones collected by 

 Professor David being due to earth-movements in a conglomerate. 



In order however that we may avoid all possible sources of 

 error we must consider the curious cases of polished floors and 

 striated fragments due to landslips. Of these I exhibited 

 examples 1 from Wales and the south of England on the former 

 occasion. The condition of the surfaces would be in many of these 

 identical with that produced by glacial action. In both cases in 

 order to produce it the stones must be in contact. The striations 

 on fragments from landslips have however a greater tendency 

 to be parallel, whereas in all glacial boulder clays it is seen that 

 the direction of the striae has been frequently changed, owing to 

 the shifting position of the stones as they have been carried 

 forward in the frozen mass and scrunched against one another on 

 a far longer journey and over a much more irregular surface than 

 in the case of landslips. 



Heim and Baltzer attach considerable importance to the 

 difference in character and effect produced by slips of superficial 

 debris (Schuttstiirze) and falls of solid rock (Felssttirze), and 

 Mr Wickham King recalls examples from the Dumberg landslip 

 near Elm in which the fallen rock produced a bruise from the 

 force of impact and a groove beyond it where the mass was forced 

 forward. Heim points out that when the soil is of a clayey nature 

 the slickensided surface is as smooth as a mirror, with fine 

 parallel striations in the direction of the movement. A still more 

 conspicuous polishing of the surface is always produced upon the 

 solid rock under the slipped mass : and sometimes it is only the 

 solid rock at the base that is polished. The polished surfaces in 

 the slipped mass generally occur in the lowest layers, and some- 

 times, instead of there being one uniform surface so polished, 

 there are several such planes succeeding one another at various 

 angles. These polished surfaces often extend with remarkable 

 constancy over very wide areas. In the channels cut to carry off 

 the water under the landslip at Villnockenn on the Bozberg 

 railway, which was of small vertical descent but of great breadth, 

 it was possible to trace a perfectly smooth surface polished like 

 glass and extending for several hectares (a hectare is something 

 under 2^ acres). 



Dr Baltzer mentions that, after the fall and slip of debris at 

 Bilten, clearly defined striations, caused by the stones in the 

 sliding mass, were observed on the upper slopes, some of them 

 running in sinuous curves. He also states that ruts, like those 

 made by the wheels of a cart, have been observed after a landslip 

 in the Suabian Alps ; and that, after the landslip of Bottstein, the 



1 Nos. 32, 33, 41, op. cit. pp. 120, 121. 



