1893.] evidence for the Recurrence of Ice Ages. 113 



The same kind of reasoning has led others' to refer certain 

 beds in New South Wales to ice agency. The earlier observers 

 Sir R. Daintree and Dr Selwyn, though the idea of the glacial 

 origin of the boulders was present to them, said, "grooved or 

 ice-scratched pebbles or rock fragments have however not yet 

 been observed." Their impression was that the character of the 

 conglomerate was very suggestive of the results likely to be pro- 

 duced by marine glacial transpo7't. The section given by Mr 

 David is not unlike what may be seen everywhere along our 

 Norfolk coast where the contortions are probably due to stranding 

 sea-borne ice. 



After a long time Oldham found "boulders and pebbles, 

 unmistakably striated and polished by ice, in a railway cutting at 

 Branxton, close to the spot where the erratics were first found by 

 Mr Wilkinson." This reminds me strongly of what happened in 

 regard to the conglomerates at the base of the Carboniferous 

 in the north of England. Not a scratched stone could be de- 

 tected in all the great boulder beds along the Lune nor at the 

 foot of Ullswater, nor anywhere until I found the belt of faulted 

 and disturbed rock near Dent, and from this an abundant supply 

 of well smoothed and striated boulders has been since obtained. 



A somewhat similar deposit has been described '"^ as occurring 

 in South Airica, and the suggestion that the boulders in it were 

 ice-borne has found increasing favour as the identification of the 

 series with the Talchir beds of India and the Bacchus Marsh beds 

 of Australia proceeded. When that view was first communicated 

 to the Geological Society I ventured to point out sources of error 

 in the observations on which such deposits had been referred to 

 glacial agency. While believing, as must any one who holds the 

 geographical theory of the origin of glacial condition, that there 

 had often in past time been local ice ages, I pointed out that the 

 mere occurrence of subangular boulders did not prove a glacial 

 origin, and that in the case under discussion the Natal deposit 

 was not like our boulder clay, but was a stratified and ripple- 

 marked series, and moreover was shown to have been subjected to 

 such pressure that distinct cleavage was produced. Of course 

 such pressure must have produced a differential movement be- 

 tween the included boulders and the matrix. 



Sometimes the form of the stones in a conglomerate rather than 

 their striation or polish is relied on. The form of the boulders in 

 glacial drift, as in water-borne accumulations, is chiefly dependent 

 upon the manner in which the divisional planes of the parent rock 



1 David, Q. J. G. S., Vol. xmii., 1887, p. 190. 



2 Sutherland, Q. J. G. S. xxvi., p. 514, 1870, ib. p. 517. Griesbach, Q. J. G. S., 

 XXVII. p. 58. Schenck, A. Pet. Mittheilimg, 1888, p. 225. Protokoll der Mdrz- 

 Sitzang. N. Jahrbuch. Stuttgart, 1889, p. 172. 



VOL. VIII. PT. III. 9 



