NATURE OF THE SEA’S RETREAT. 119 
Yet notwithstanding these difficulties it certainly 
seems that the appearances of the ancient beach 
of Plymouth Hoe, and the identity of the animals 
connected with it with those now existing, provide 
for it a relative date,—an age separate from, and 
indeed posterior to, that of the cave-animals. 
To resume :—With respect to the retreat of this 
tide, Lconceive that if it had been by successive steps, 
these beaches around the cliffs of Devon and Corn- 
wall would certainly be traceable downwards to 
the present ones, which they cannot; and it is 
accordingly probable, that as the movement of the 
land in its retreat must have been dependent on a 
similar cause to that which produced its ingress, 
both actions were accomplished in one manner, 
namely by quiet, continuous subsidence, and quiet 
and continuous elevation. 
To trace this retreating tide to its ultimate level 
is a matter of no small difficulty, because it appears 
that during the last centuries, the sea throughout 
the whole of the northern countries has been con- 
tinuedly falling from the land, besides which, an 
effect of no mean magnitude is exerted on the bulk 
of our neighbouring sea by the great diminution in 
the size of our estuaries and inlets,and athird power 
of an opposite character to the two former consists 
in the vast bulk of the Atlantic waves which are 
perpetually driven towards the south-western parts 
of England,—tending to increase somewhat the pro- 
portion of sea by which they are encompassed. So 
that, whilst the accumulations of alluvial matters in 
our estuaries, and the diminished bulk of our 
rivers as compared to their ancient condition, and 
the gradual sinking of the ocean from the coasts of 
northern countries, would inevitably tend to reduce 
the height of our tide very greatly, a partial coun- 
terpose to this reduction is afforded by the pressure 
of the Atlantic wave which especially in more 
