J. R. Dakyns — Sediment Theory of Drift. 



171 



We have already shown that there is no evidence of continental ice 

 from afar. Must we not then conclude that the grooves were caused 

 by floating ice continually scraping along the submerged land ? 



About the transport of erratics I will not speak, as I have no 

 evidence to offer on the subject: but this much I must say, that if 

 it is the general rule for moving ice to carry unbroken such fragile 

 substances as shells or glass bottles, the vast number of rounded 

 stones in the Drift is more inexplicable than ever. 



The question too of counter currents in the ice I leave to those 

 who are better acquainted than I am with the physics of ice. But 

 if I understand Mr. Groodchild aright, his idea involves the fallacy 

 of perpetual motion : for in the figure below, the dotted arrows 

 indicating the course in the ice of any boulder, say from X, current 

 A sets outward (from the lake mountains suppose) carrying boulders 

 from the centre of the district up to the point where it meets with 

 B (a current from Scotland suppose), and is turned back again at 

 a higher level. Boulders of X are worked up to Y : then when the 

 ice melts, they are melted out as a kind of sediment, and left at Z. 



This, I conceive, is how Mr. Goodchild would explain the fact 

 that " even in those parts of the Lake District in which the majority 

 of the boulders have moved outwards at low levels, we find that 

 some of the very same rock has been transported in opposite direc- 

 tions towards the heart of the mountains," to wit, " by the strong 

 upper currents which were setting in from Scotland." So far so 

 good. But in the case figured, boulder X arrives at Y so late that 

 the ice is then on the point of melting away entirely, and it quietly 

 subsides to Z. But what of a similar boulder which sets out earlier 

 on its travels, and reaches the point Y, say, at the height of the 

 Glacial Period ? — what becomes of it ? It must go somewhere. It 

 must surely get again into the outward current A, and be carried 

 back nearly in its old course, and so go on revolving as long as the 

 ice lasts. There is no escaping this impossible conclusion, unless 

 we suppose either that the Scotch ice B went clean over the Lake 

 mountains on the top of their native ice, or that the conflicting 

 currents flowed away right or left laterally to the low ground. 

 There is not a particle of evidence to show that the Scotch ice went 

 over the Lake mountains. If then the conflicting currents flowed 

 away laterally, why should there be any over-riding at all? On 

 meeting, the stronger current would dam back the weaker one till 

 a position of equilibrium was attained ; and thenceforth the two 

 currents would flow away literally in a united stream according to 

 the fall of the ground. 



