14 ME. J. E. MARE ON A CONGLOMEEATE [Feb. 1 899, 



Discussion. 



Sir A. Geikie, being called upon by the President, remarked that 

 not having any acquaintance with the locality or the specimens 

 described by the Author, he hardly felt himself in a position to 

 offer any remarks upon them, but lest his silence should seem to 

 imply any want of appreciation of the interest and ingenuity of the 

 paper, he would gladly admit that in his opinion the Author had 

 completely proved the point sought to be established. The peculiar 

 features of the conglomerate described in the paper were obviously 

 due to earth-movements, and not to glacial action. At the same 

 time, while frankly admitting the explanation of the case now 

 brought forward, he held that conclusive evidence had been obtained 

 of glacially-striated boulders in old geological deposits. Instances 

 of these had in recent years been brought before the Society, and 

 while he accepted them, he was also prepared to believe that 

 innumerable examples might be adduced in which the stones in 

 conglomerates had undergone striation in situ by earth-movements, 

 and had thus acquired a most deceptive resemblance to boulders 

 smoothed and striated by ice. 



Dr. W. T. Blanfoed said that if anyone had produced the speci- 

 mens on the table as evidence of glacial action, the Author would 

 probably have been sceptical and would, in the speaker's opinion, 

 have been quite justified in his want of faith. The occurrence of 

 boulders and pebbles embedded in a fine silt was better evidence of 

 glacial action than scratched surfaces, and it was upon the former 

 that the belief in a Carboniferous glacial period in the Southern 

 Hemisphere and India was originally founded. The speaker did not 

 ^ think that there was any similarity between the surfaces produced 

 by wind-action and ice-action respectively. 



Prof. SoLLAS agreed with the Author's interpretation of the 

 markings exhibited. They were evidently r u t s c h- striae and slicken- 

 sides, and presented no unusual characters. There should be no 

 difficulty in the present state of our knowledge in distinguishing 

 between such phenomena and glaciated surfaces. On the peninsula 

 of Howth, near Dublin, projecting knolls of rock bore markings of 

 both kinds, those due to earth-movements and those resulting from 

 the movement of ice; but it was always possible to discriminate 

 between them. 



Prof. Watts found it difficult to conceive how any conglomerate 

 which had passed through earth-movement could escape having its 

 pebbles striated. Less stress was now being laid on the value of 

 striae to indicate former glacial action, and perhaps the time was 

 coming when less importance would be attributed to the shape of 

 the fragments and their derivation from a distant source. 



Mr. H. W. MoNCKTON thought that the specimens on the table 

 could scarcely have been supposed to furnish evidence of glacial 

 action, whether taken singly or all together. He referred to a recent 

 paper in which evidence in favour of glacial action in Palaeozoic 



