92 Erratic Phenomena about Lake Superior. Pe tke 
More recently, a step towards the views I entertain of this sub- — 
_ ject, has been made by those geologists who would ascribe them ~ 
to the agency of icebergs. Here, as in my glacial theory, ice “ me: 
made the agent; floating ice is supposed to have ground and pol-. | 
ished the surfaces of rocks, while I consider them to have been ~ Bs. 
acted upon by terrestrial glaciers. To settle this difference we 
have a test which is as irresistible as the other arguments already 
; introduced. 
Let us investigate the mode of action, the mode of transport- 
ation of icebergs, and let us examine whether this cause is ade- e. 
1 
hills, and in depressions of the soil, and the scratches whic 
over such undulating surfaces are nevertheless continuous in 
straight lines. If we imagine icebergs moving upon shoals, no 
doubt they would scratch and polish the rocks in a way similar 
to moving glaciers. But upon such localities they would sooner 
or later be stranded, and if they remained loose enough to move, 
they would, in their gyratory movements, produce curved lines, 
and mark the spots where they had been stranded with particular ; 
indications “i their prolonged action. But nowhere upon arctic, - 
round do we find such indications. Everywhere the polished | 
and oie surfaces are continuous in straight juxtaposition. 
Phenomena analogous to those produced by icebergs would 
only be seen along the sea-shores; and if the theory of drifted 
icebergs were correct, we should have, all over those continents 
where erratic phenomena occur, indications of retreating shores 
as far as the erratic phenomena are found. But there is no such 
thing to be observed over the whole extent of the North Ameri- 
can continent, nor over Northern Europe and Asia, as far as the 
northern erratics extend. From the arctics to the southernmost 
limit of the erratic distribution, we find nowhere the indications 
of the action of the sea as directly connected with the production 
of the erratic phenomena. And wherever the marine deposits 
rest upon the — —— of ground and scratched rocks, 
they can be shown to be deposits formed since the grooving and 
polishing of the sii in saunas of ee ee of those 
tracts of land upon which such deposits oc 
Again, if we take for a moment into ccusidaletien the immense 
_ extent of land covered by erratic phenomena, and view them as 
produced by drifted icebergs, we must acknowledge that the ice- 
rgs of the present period at least, are insufficient to account for 
them, as they are limited to a narrower zone. And to bring ice- 
bergs in any way within the extent which would answer for the 
extent of the distribution of erratics, we must assume that the 
northern ice fields, from which these icebergs could be detached 
and float southwards, were much larger at the time they prod 
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