1877*] The Great Ice Age and Origin of the “ Till .” 237 
of till just grazing the bottom of the glacier ? Obviously to 
wash away the fine clayey particles, and leave behind the 
coarser sand or gravel. It must form just such a basin or 
lenticular cavity as Mr. Geikie describes. The oblong shape 
of these, their longer axis coinciding with the general course 
of the glacier, would be produced by the onward progress of 
the moulin. The accordance of their other features with 
this explanation will be seen on reading Mr. Geikie’s descrip- 
tion (pp. 18, 19, &c.). 
The general absence of marine animals and their occa- 
sional exceptional occurrence in the intercalated beds is just 
what might be expected under the conditions I have sketched. 
In the gloomy subglacial depths of the sea, drenched with 
continual supplies of fresh water and cooled below the 
freezing-point by the adfion of salt water on the ice, ordinary 
marine life would be impossible ; while, on the other hand, 
any recession of the glacial limit would restore the condi- 
tions of ardtic animal life, to be again obliterated with the 
renewed outward growth of the floating skirts of the inland 
ice mantle. 
But I must now refrain from the further discussion of 
these and other collateral details, but hope to return to them 
in another paper. 
In “ Through Norway with Ladies ” I have touched 
lightly upon some of these, and have more particularly 
described some curious and very extensive evidences of 
secondary glaciation that quite escaped my attention on my 
first visit, and which, too, have been equally overlooked by 
other observers. In the above I have endeavoured to keep 
as nearly as possible to the main subjedt of the origin of 
the till and the charadter of the ancient ice-sheet. 
