near St. Andrews. 203 
_ plants, with some of the stems in an upright position, There 
were likewise numerous fibres and rootlets of seemingly various 
plants. These rootlets and impressions clearly indicate that 
marshy and perhaps other plants had at one time grown in 
abundance on this bed; and, so far as observed, this would ap- 
pear to have been before the third bed was laid down, as no 
rootlets or stems could be seen in that deposit ; and there seems 
no reason why they should not have been preserved, or traces of 
them, in the one bed as well as in the other, if they had ever 
been there. No doubt, from the littoral character of the shells 
found in this bed, some of them could exist although they were 
not many feet under water at every tide. Some of the Telline 
can live high upon the muddy shores of estuaries; so can Scro- 
bicularia. And, from the large size of these species, it may 
be inferred that they had found a more congenial habitat than 
seems to have been the case with Mytilus and Cardium, whose 
size and thickness might at the same time be somewhat influ- 
enced by the freshness of the water. The three latter species 
can undoubtedly live in places where the water is as often fresh 
as salt. Jeffreys says* that the Mussel and the common Peri- 
winkle (Littorina littorea) are occasionally found living on the 
shore in a stream of perfectly fresh water during the recess of 
the tide, that Cardium edule has the same habit, and that the 
latter species even occurs associated with freshwater Mollusca. 
It is well known, from the writings of Montagu and others, 
that Scrobicularia piperata burrows in muddy places that are 
occasionally covered with fresh water, at the mouths of rivers, 
or far up estuaries. So far as my own observations go, the 
shell of the latter species retains nearly its normal size and 
thickness in places where neither Cardiwm nor Mytilus seem 
capable of existing, or, if met with, are always in a thin and 
dwarfed state. However, there can be no doubt that all the 
foregoing species could not have lived in situations so high 
above the sea as to allow even marshy plants to grow. This 
being the case, the plants must have grown after the bed was 
raised a few feet higher above the water. For this purpose 
one of two causes would be necessary: either the land at this 
time was slowly rising, or the estuary was gradually silted up: 
perhaps both these operations were going on at the same time, 
although it would be impossible in the present instance to say 
which had the chief hand in the matter. At the same time that the 
land was elevated to some extent, there seems no room to doubt 
(indeed, according to the observations of Geikie+ and others, there 
appear good reasons for believing) that the land on many other 
* British Conchology, vol. ii. 
+ The Glacial Drift of Scotland. 
