270 Rev. T. G. Bonney — Ice- Scratches in Derhyahire. 



ficial film, than as an intimate part of the rock, reminding one of the 

 way in which slickenside galena is occasionally found. A close ex- 

 amination of the striae showed — after discarding some which may 

 safely be ascribed to the hobnails of 'historic ' men — that they were 

 rather flutings in, than scratches on, a polished surface ; that is, that 

 the small grooves themselves were polished : one of the best dis- 

 tinctions that I know between slickensides and ice-striae in hand 

 specimens. Again, it was very hard to understand how two such 

 perfect surfaces could coexist if they had been produced by berg or 

 glacier. Both occurred on exposed spots in juxtaposition, well de- 

 veloped, one might say brightly polished. They could not have been 

 simultaneously produced. How then did the former set escape 

 obliteration, or at least great injury, during the production of the 

 latter ? We cannot explain this by the well-known fact that stones 

 in boulder deposits often have more than one set of markings ; for 

 these are mere scratches, unaccompanied by a corresponding polish- 

 ing of such a hard surface as bhert. But two or three different planes 

 of slickensides do coexist in the same mass of rock. On closely 

 examining the polished surfaces on the Bloody Stone, I observed 

 that occasionally they appeared to dip into the rock, suggesting that 

 if we broke it (which I did not think it right to do) we should find 

 them pervading the mass. Again, I found in the middle of a surface, 

 striated in one direction, an irregular pit or depression, produced 

 apparently by a part of the rock having flaked off, in which the 

 striae ran in the other direction. (Mr. Green, by careful measure- 

 ment, made out three directions of striation, two of them, however, 

 are sufficiently near together to produce the general impression of 

 two directions only, one roughly down, the other athwart the valley.) 

 Now the polished surface could in these cases be sometimes traced 

 quite close to the inclosing wall of the depression, which was 

 occasionally nearly half an inch high. I also found the polishing 

 more than once quite close to the foot of small, rough, projecting 

 knobs of chert. Indeed I may venture to say that I found the 

 polished striations in four or five places at least where a large mass 

 of ice could not have produced them. In short, there was something 

 in the general appearance and mode of occurrence of the markings 

 which, though it can hardly be explained in words, was to my eye 

 not consistent with their being ice-marks, and with these I happen 

 to be very familiar. 



About 30 feet lower down on the hill-side the adit of a mine has 

 been begun. I examined this, and found within the entrance, and 

 so, undoubtedly, in the mass of the rock, a set of slickensides on 

 chert, running roughly north and south, and in a plane inclined at a 

 small angle with the vertical, and so not far from at right angles 

 with the surfaces in which the others occur. 



I am, therefore, driven to the conclusion that these curious mark- 

 ings are not ice- striae, but slickensides ; though, so far' as my ex- 

 perience goes, a very unusual instance of this structure, and suppose 

 that it must have been exposed in making or enlarging the road, 

 which runs exactly over the boss of rock. 



