34 R. D. Oldham — Facetted Pehhies from the Punjab. 



vents us from ascribing their origin to a movement of the soil-cap, 

 while the steadiness of direction of the strise on each face shows 

 that the fragment mnst have been firmly held, and, in the case of 

 the SQialler ones, it is difficult to see how they could have been so 

 held except by being imbedded in some material which, like ice, 

 would adapt itself completely to the shape of the pebble. 



The striated faces bear no resemblance to slickensides, and as the 

 fragments seldom touch each other in the bed, but are separated by 

 a greater or less thickness of the fine-grained matrix, any attempt to 

 explain their origin by friction of the pebbles against each other 

 subsequent to deposition is inadmissible ; moreover, there is no 

 exceptional disturbance of the beds, and the striated fragments are as 

 common where they lie nearly horizontal as where they are tilted. 



The only other agency by which the facets could have been pro- 

 duced is that which is at first sight suggested by the appearance of 

 the pebbles, viz. ice, and it only remains to see whether this was in 

 the form of coast-ice or glaciers. Here we must leave the domain of 

 certainty, and enter on that of probability. 



Prof. J. Milne has shown ^ that, as far as the live rock is concerned, 

 many of the appearances usually considered characteristic of glacier 

 action may be produced by coast-ice ; but in the present case we are 

 not concerned with what happens to tlae rock in situ, but with the 

 effect produced on the loose pebbles and boulders caught up in the 

 ice and ground on the solid rock. At first sight the number of 

 striated faces on many of these pebbles would seem to point to the 

 action of coast-ice, for, after every melting of the ice, the pebble 

 would probably be fixed each winter in a fresh position, and offer a 

 different face tor abrasion ; but it is doubtful whether the facets do 

 not indicate a greater pressure and a greater constancy of direction 

 of motion than could be given by coast-ice, and it is still more doubt- 

 ful whether they could be produced during a single winter, which on 

 this supposition is all that can be allowed for each facet. 



A much stronger objection is the entire absence of any sign of the 

 action of water on some of the pebbles. Had the facets been due to 

 the action of coast-ice forming in winter and melting again in 

 summer, the pebbles would every year have been exposed for a longer 

 or shorter time to the action of waves, and the sharp, clean-cut 

 junction of the facets which we find would have been more or less 

 abraded ; so that, if the shape of these pebbles is due to the action of 

 coast-ice, it must have been perennial. I need but point out that 

 coast-ice lasting through winter and summer implies a much severer 

 climate than is needed to account for glaciers descending to the sea ; 

 a priori then the latter is the more probable hypothesis as requiring 

 the least climatic change, besides being more in consonance with the 

 evidence derived from the appearance and mode of occurrence of the 

 boulders and pebbles showing signs of glacial action. 



I have now shown that these boulder beds owe their origin 

 primarily to the action of floating-ice, that the shape of the facetted 

 fragments must be due to glacial action, that some at least of them 

 1 Geol. Mag. Dec. II. Vol. IV. p. 293 (1877). 



