MANCHESTER GEOLOGICAL SOCIiLi f. 
125 
been reduced to an impalpable powder. To what cause, then, it 
may be asked_, are we to refer the transportation of erratic 
blocks ? To a circumstance which still continues to operate 
even at the present time^ viz. the transportation of rocks and 
earthy matter, by icebergs, which have originally -been portions 
of arctic glaciers. These icebergs have_, during their existence 
as parts of the arctic glaciers^ detached portions of rock from 
the mountains on whose side they rested_, by the dilatation of. 
their mass^ effected by the congelation of infiltrated water ; and, 
after being separated from their parent glacier, have, by the in- 
fluence of currents and v/inds, been carried to a more temperate 
latitude^ where they have deposited their foreign matter, in con- 
sequence of the action of solar heat ; and most probably pro- 
duced on the bed of the ocean a formation very much resem- 
bling the erratic block deposit. 
" This conclusion which necessarily supposes icebergs to have 
been transported to localities where they are now never found, 
is supported both by Agassiz and Smith, who believe that, at a 
very recent geological epoch, the fauna of Great Britain partook, 
to a great extent, of an arctic character. Agassiz is of opinion 
that some of the shells which are now found in the post-tertiary 
deposits, no longer exist in a living state in the neighbouring 
seas, but are confined to habitats at least from twelve to fifteen 
degrees of latitude to the north. Thus, for instance, the shells 
of Greenland and Iceland are found fossil in the post-tertiary 
deposits of England and Scotland. The mollusca, which are 
now living on the coast of England, have had types living during 
the post-tertiary epoch on the coasts of Sicily. 
From these observations of Agassiz, it is evid^jnt that the 
British Isles possessed, during the post-tertiary period, a climate 
similar to Iceland ; and that, from the declivities of the British 
mountains, glaciers frequently spread themselves along the sur- 
face of the sea, and, becoming detached, formed icebergs, which 
transported worn and polished blocks, derived from the mouu- 
