NATURAL HISTORY OF THE BANKS OF THE TAY. 
45 
We now commence our epitome of the geological history of the 
true “Alluvial” or recent deposits of the Tay basin, which, with all 
the manifold changes that have come about since the recession of the 
glaciers, are all characterised by the presence of a recoit fauna and 
flora. 
It is quite unnecessary to suppose, as many geologists have done, 
that the change from glacial conditions to those of our recent epoch 
was accompanied by any extraordinary or exceptional phenomena. 
On the contrary, all the evidence seems to point to what we may call 
natural conditions—to such conditions, indeed, as may be found in 
some parts of Europe at the present day. The glaciers receded from 
our country, as they had encroached upon it, by slow and impercept¬ 
ible degrees. The transition was simply one from flowing rivers to 
slowly gliding ice, and then from ice to flowing rivers again. We 
now, therefore, take up the story of the work of the river, begun when 
the last of the glaciers had gone from the mountains. In considering 
the geological work of the river it is well to bear in mind that we are 
dealing with an agency whose operations are familiar enough, but 
whose power and capacity are too apt to be under-rated by the 
geologist. 
Rivers are not only streams of water flowing down to the sea, but 
they are, and always have been, the creators of order and beauty on 
the face of the earth. Where our history of the Tay valley now 
begins, they were the means of restoring order and beauty to a por¬ 
tion of the country where desolation and chaos had reigned before. 
The first function of the reinstated rains, streams, and rivers, was that 
of breaking the shapeless and impeding masses of broken rocks and 
crushed debris^ and distributing them far and wide upon the level 
plains and valley floors. This was, ere long, accomplished, by pro¬ 
cesses which the proportions of this paper will not allow us to discuss. 
Thus, hill slopes were shorn of their more rugged masses, the 
materials of which, finding their way down to the greater valley 
floors, were re-distributed by the levelling, assorting, and construc¬ 
tive capacity of the river. This being accomplished, the valleys 
once more became green and beautiful, as they had been in the 
times preceding the inception of cold conditions. 
When this had been achieved, the work of the river may be said 
to have only begun, for even after the beauty of the valley floor had 
been restored, every heavy rain would bring down upon it a portion 
of the superabundant glacial material still remaining on the higher 
ground. This condition of matters continued for a lengthened 
period of time, and produced results which have left their mark on 
the configuration of the Tay valley at the present day. These 
conditions, which have not hitherto been generally recognised by 
