MEMORANDA. 61 
of the occurrence of so many marie forms in an inland 
deposit, formed in a fresh-water lake, is this: that at the 
period when the sand was formed the relative levels of the 
Dhu Loch and of Loch Fine were the same as now, when 
similar results ensue. 
“ But as the lake was then at a higher level than now, so 
also must the sea have been at a level as much above its 
present one. This conclusion is in accordance with those 
derived from the observations made on raised beaches on the 
banks of the Firth of Clyde, the level of which must always 
have regulated that of Loch Fine since the present form of 
the coast has existed. 
«There was, however, a circumstance which at first tended 
to throw some doubt on this conclusion, according to which 
the marine forms of the Glenshira sand must have come 
from Loch Fine. For although the known and described 
marine Diatoms found in the sand occur on our coasts, yet I 
was struck with the fact that out of upwards of fifty new or 
undescribed forms, there seemed to be no trace in deposits 
from the Firth of Clyde, examined by more than one natu- 
ralist during the progress of my investigation. The fact of 
these forms being undescribed was prima facie evidence that 
they had not occurred on the British coasts. 
“Yet it was evident that the formation of the Glenshira 
sand, was, geologically speaking, very recent; so recent, 
indeed, that we could not suppose.any number of species 
to have since become extinct. I came, accordingly, to the 
conclusion, that these undescribed forms must still exist in 
the waters of Loch Fine, or, what is the same thing, of the 
Firth of Clyde. I was therefore desirous to examine with 
care deposits from these waters, and this, during the past six 
months, I have been enabled fully to do. 
“The materials which I have examined are the follow- 
ing : 
“1. A small quantity of dirt or sand washed from some 
nests of Lima hians, dredged in Lamlash Bay on the 19th 
of July last, in four fathoms, by Professor Allman. This 
material, though, when cleaned, very scanty, proved the 
richest of all. 
2. Four dredgings, made by myself, with the kind assist- 
ance of the Duke of Argyll, in Loch Fine, at different 
points within two or three miles of Inverary. These were 
all different, and three of them were interesting. They were 
taken at dephts of from fourteen to eighteen fathoms, early 
in October. 
