1872,] TIDDEMAN ICE-SHEET IN NOKTH LANCASHIRE ETC. 487 



cier, and the impetuous swirling torrent wliicli enters it at mid- day 

 hurrying down stones from the surface of the ice, can doubt that there, 

 at any rate, is a mill in which rolled pebbles are being manufactured ; 

 and such "moulins" must have existed in abundance on the ice-sheet 

 in the times of its decay. 



IV. CoNCLtrSIONS. 



I have endeavoured to show that in the district with which I am 

 more intimately acquainted, there are proofs of a widespread and 

 almost universal glaciation — that whereas the drainage of this district 

 is to the S.W., the general movement of the ice over it was to the 

 S. or S.S.E. across deep valleys, and over hills of considerable eleva- 

 tion — that this is proved by the scratches on the rocks, the direction 

 and method of transport of the TiU, its materials, and their arrange- 

 ment along lines coinciding with the scratches, as well as by the 

 superficial disturbances of the rocks. I showed that these facts 

 would admit of readier explanation by means of an ice-sheet than by 

 any other glacial agent. J3ut the direction of the movement requires 

 a further explanation. Under ordinary circumstances an ice-sheet 

 would be working down from the watershed to the sea in the direc- 

 tion of the main valleys ; but this was not so. There must have 

 been a great barrier along what is now the seaside plain to dam up 

 the mouths of these valleys to a great height and prevent their dis- 

 charge of ice to the south-west. Just where this barrier should have 

 existed we find evidence of a great stream of ice coming from the Lake- 

 district and bearing with it rock-specimens of that country. This 

 must have been of considerable height and very persistent in its flow 

 to divert the ice-drainage of the basins of the Lune and the Eibble from 

 their natural course ; but that it did so is very evident. This barrier 

 was but the line of junction of the ice of the Pennine chain Avith 

 that from the Lake-district, and to the eye they must have presented 

 only the appearance of one great sea of ice ; and this barrier must 

 have been supported or shouldered up by other ice coming from por- 

 tions of the Lake-district stiU further west. 



After coming to the above conclusions I could not fail to be 

 interested in finding how thoroughly the facts observed by the 

 Eev. J. G. Gumming in the Isle of Man agreed with those which 

 I had met with in North Lancashire and Yorkshire. Mr. Gum- 

 ming, in his work ' The Isle of Man,' states that the glacial scratches 

 have an almost uniform direction across the island of magnetic east 

 to west, that is from the E.N.E. In speaking of the very local 

 character of the lower portion at least of the Boulder-clay forma- 

 tion, he says (p. 113), -'as we proceed westward we shall observe 

 how it changes in composition and tallies in chemical character, as 

 well as in lithological appearance and colour, with that of the sub- 

 jacent prevailing rock a very little to the eastward of any spot on 

 which we may fix for its examination." Further on, p. 120, he says, 

 " we fall in with pebbles of foreign rocks in the Boulder-clay which 

 must have come from a great distance, from the shores of Cumberland 

 and the south of Scotland ; " and this leads him " to the conviction of 

 one great current setting down from the Solway Prith upon these 

 shores and overpowering the effects of local currents caused by the 



