Mollusca of the Laminarian Zone at Leith, 341 
There is no reason why, with the amelioration of the climate 
that has followed the Glacial Period as a consequence of the 
subsidence referred to, the Mollusca found at Leith, for 
example, should not closely correspond with those still 
found, under similar conditions of bottom and depth, off the 
north-west of Scandinavia. Or, if that were not the case, we 
might reasonably expect a transition in the character of the 
molluscan fauna as the strata representing the deposits of 
the successive periods are traced from those of the Glacial 
Period up to those lately found at Leith. This, however, is 
not the case. At Leith, instead of there being a transition 
in petrographical character from the deposits of glacial age 
up into those of later date, and a similar transition in the 
respective faunas, we find the sands which overlie the 
boulder clay there succeeding the boulder clay abruptly and 
without any signs of a passage, while the molluscan fauna of 
the sands referred to (which are from 12 to 15 feet in 
depth, according to the form of the surface upon which the 
sands lie) is from bottom to top virtually the same, and 
contains, in fact, exactly the same kinds of shells as those 
living on a sandy bottom from low-water mark to a depth of 
3 or 4 fathoms in the Forth now. 
What has happened is not difficult to explain. As the 
elacial conditions gradually died away, and deposits of the 
normal type began to be laid down upon those formed under 
arctic conditions, there has been a tendency for the land as a 
whole to rise towards the level it had in former times. With 
each uprise of the land the gradient of the bottom of the 
Forth has been increased proportionately with the differ- 
ence of level established, and an increased flow has been 
imparted to the bottom-waters, with the result that one 
deposit after another, together, of course, with their included 
organic remains, has been swept seawards and rearranged. 
The formations contemporaneous with each of the newer 
raised beaches (which deposits might have been expected to 
contain records of the life of each of these periods) have been 
one after the other swept away. The boulder clay itself 
being probably very thick to begin with, and being, moreover, 
excessively tough and difficult of removal, has in great part 
