( 35 ) 
On the Post-tertiary Diatomaceotis Sand of Glenshira. 
Part II. Containing an account of a number of additional 
undescribed species. By William Gregory, M.D.,F.R.S.E., 
M.R.I.A,, &c. ; Professor of Chemistry in the University 
of Edinburgh. Illustrated by numerous figures drawn from 
Nature, by R. K. Greville, LL.D., F R.S.E., &c., and 
engraved by Tuffen West, Esq. (Plate V.) 
(Read March 26, 1856.) 
In the first part of this communication * I described the pecu- 
liar locality in which the Glenshira Sand occurs, and pointed 
out, that the remarkable mixture of marine and fresh water 
forms which it contains, was a proof that, when this sand or 
mud was deposited, the fresh« water lake, then filling the 
upper part of the valley, and standing, of course, at a higher 
level than it now does, must yet have occupied the same 
relative level, compared with the sea, which it now occupies, 
when it is confined to the lowest part of the valley, and being 
exactly at the level of half-tide, flows into the sea at low 
water ; while, at high water, the sea flows into the lake. This 
state of matter produces in the lake, at this moment, a mix- 
ture of marine and fresli-water species, not only of diatoms, 
but also of other tribes, both animal and vegetable. And as 
the existence of a similar mixture in the sand now under ex- 
amination, deposited at the higher level, implies that at the 
period of its deposition the relative levels of the sea and of 
the lake were the same as now, while we see that the lake 
now stands at a lower level than formerly, we infer, that since 
that period the land has risen, or the sea has fallen ; a con- 
clusion justified and supported by many other geological phe- 
nomena in the estuary of the Clyde, with which Loch Fine, 
the arm of the sea into which the Dhu Loch of Glenshira 
flows, communicates. 
In the same paper I gave a list of about 215 known species 
of Diatoms, and nearly 20 undescribed species, which I had 
found in the deposit ; a number of species far exceeding that 
hitherto found in any other similar deposit, so far as is known 
to me. This, I conceive, indicates that the circumstances 
which favoured the mixture and accumulation of species must 
have been of very prolonged duration. 
At the same time I stated that there remained about as 
many more undescribed forms as those I had been able at that 
time to figure, and that these should be figured and described 
on some later occasion. I now proceed to fulfil that promise. 
I must explain, however, that it is impossible for me to com- 
♦ * * Quarterly Journal of Microscopical Science,' vol. iii., p. 30. 
VOL. IV. e 
