219 



Criticism of the Geological evidence for the Recurrence of Ice 

 Ages'. By T. M^Kenny Hughes, M.A., F.KS. 



Part II. (For Part I, see p. 98.) 

 The Mode of Transport of Boulders and other Drift. 



Having considered the nature of the evidence which is relied 

 upon in proof of the glacial origin of the fragments included in 

 certain clays and conglomerates and having exhibited a large 

 collection of rocks polished and striated in different ways, both 

 natural and artificial, but known to be unconnected with glacial 

 action, and having endeavoured to indicate the points of resem- 

 blance and of difference between these and the undoubtedly 

 glaciated surfaces, I now go on to consider other sources of error 

 in the observations upon which we have to rely before we attempt 

 to construct a natural explanation of the phenomena of recurrent 

 glaciation^. 



That the boulders were left hy the ice in the place lohere they 

 notu lie is not always to be received with unquestioning faith. 

 In hurried explorations and especially in those of remote regions 

 the observers can rarely be expected to be familiar with all the 

 operations of nature which move and bury blocks in each par- 

 ticular district and we may admit that landslips or mudflows or 

 the many other processes such as we commonly see on a coast 

 like that of Norfolk', with its cliffs of various drifts, may fre- 

 quently have resulted in the burial of transported material in 

 unexpected places and in positions difficult of explanation. 



We have to enquire not only how nature moulds and sculptures 

 the stones on which we rely for evidence of glacial action but also 

 how far the occurrence of a boulder clay containing such stones, 

 even when associated with marine beds, necessarily implies 

 glaciers coming down to the sea in the area in which the boulder 

 clay is now found. 



If any region, in which glaciers were generated on the high 

 ground and descended to within say 5000 or 10,000 feet only of 

 sea-level, were afterwards depressed to that number of feet, the 

 glaciers would be gone, but the moraines of those glaciers might 

 often be covered by marine deposits, and cliffs of boulder clay 



1 See page 142. 



2 Since writing the above I have had an opportunity of examining a striated 

 rock from the Indian boulder-beds which is preserved in the museum at Zurich. 

 I was satisfied from an examination of the specimen itself that the markings on it 

 were not due to glacier action, an opinion in which Heim fully concurred. 



^ See Nature, Vol. 50, May 3, 1894, p. 5. " On Some Sources of Error in the 

 Study of Drift." 



VOL. VIII. PT. III. 17 



