DRIFTS OF THE VALE OF CLWTD. 



77 



clay with boulders in it, it is required for current language. So the 

 word drift is required for common use in the sense of transported 

 superficial deposits not being volcanic ejectamenta, or rock decom- 

 posed in place, or otherwise included by more strict definition. 



What seems certain is that, starting in the Arenig district, we 

 find an ancient boulder-clay which contains no fragments from any 

 other district, and no trace of marine action, but follows the tracks 

 of the land-ice away to the east. Whether we are right in referring 

 to the same age and origin certain isolated patches of boulder-clay 

 which occur at the base of all the marine drifts of the north-east of 

 Wales and its borders, is another question ; but it seems to me that 

 there is a strong a priori reason for expecting that^such patches 

 should be left here and there, and much evidence that they have 

 been detected in some cases. Besides the sections described above, 

 in which there seems reason to suspect its existence, I may appeal 

 to the publications of many other observers for the occurrence of 

 an older, probably land-ice drift, underlying the marine drifts of the 

 same or adjoining districts. See : — 



Eyton. Geol. Mag. vol. v. p. 349. 



Hall. Geol. Mag. vol. vii. p. 509. 



Mackintosh. Geol. Mag. vol. ix. p. 15 ; Quart. Journ. Geol. Soc. 

 vol. xxix. (1873) p. 355, footnote ; vol. xxxiii. (1877) p. 738. 



Mellaed Reade. Quart. Journ. Geol. Soc. vol. xxx. p. 27 ; 

 vol. xxxix. p. 83 ; vol. xli. p. 102. 



De Rance. Proc. Geol. Assoc. vol. iv. p. 221. 



Steahax. Mem. Geol. Survey, " Geology of the coasts adjoining 

 Rhyl, Abergele, and Colwyn ; " Quart. Journ. Geol. Soc. 

 vol. xlii. (1886), pp. 36, 37. 



This drift cannot be traced continuously to the east or north 

 into the drifts of which the succession, local or general, has been 

 made out. We follow it to the margin of the Cheshire plains ; but 

 where it ended is not so clear. It is everywhere covered by newer 

 deposits over the low ground around the mountain-group from 

 which it came. Mr. Mackintosh has traced what he considers to be 

 the " junction of the Arenig felstone and Eskdale granite dis- 

 persions " along the hills north of Llangollen (Quart. Journ. Geol. 

 Soc. vol. xxxv. 1879, p. 425; vol. xxxvii. 1881, p. 361); and 

 Mr. Searles Wood, chiefly from the evidence collected by Mr. Mackin- 

 tosh, believed that the Arenig ice terminated somewhere along that 

 line (ibid, footnote). But whether left by the Arenig ice at an 

 earlier stage of further eastward extension, or derived from its 

 terminal boulder-clays during the period of submergence, there is 

 no doubt that the Arenig rocks occur in the drifts far over central 

 England. 



It is difficult to correlate land-ice drift with marine. Moreover the 

 oldest drifts of East Anglia show such a preponderance of northern 

 material that we must suppose that, although we may find there 

 drift of approximately the same age, it belongs to a different ice-= 

 stream. How the various parts of such a sheet turn round the hills, 

 cross, overlap, and, in the greater strength of one or other mass, 



