98 
Gregory on Diatomaceous Earth. 
I find I have omitted to notice that, besides the Diato- 
maceous organisms, the Mull earth contains abundance of the 
long spicules, and also of the gemmules of Spongilla fluviatilis 
and S. lacustris, also a considerable number of siliceous forms, 
apparently PhytoUtharia^ more particularly Lithostylidium 
clepsammedium, and similar forms. There are also some 
silicified forms much resembling certain deposits in the cuticle 
of Gramineze, &c., besides occasionally silicified pollen grains, 
belonging both to grasses, and as I believe to Coniferae. I have 
also seen some fragments of woody fibre and cells, probably 
silicified ; but I have not the means of determining with any 
accuracy these various organisms. Probably many members 
of the Society will be able easily to do this. I think I have 
seen some forms which resembled very much the Desmi- 
diaceae, such as Euastrum^ Staurastrum, and Cosmarium; but 
on these points I will not venture to assert anything, although, 
as Desmidiaceae occur in flint, and often contains a little 
silica, this occurrence is possible. 
In conclusion, even the imperfect examination to which 
the Mull deposit has been subjected, proves it to be richer in 
Diatomaceous species, and I think also in genera, than any 
other known deposit, so far as I am acquainted with them. 
I have heard that the deposit at Santa Fiora contains 39 
species, and that found near Peterhead, and described by Dr. 
Dickie, contains 40, but I know of no others which equal 
these two, whereas in the Mull earth we have at least 60 
species and 16 genera. This will of course be interesting in 
reference to the geographical distribution of fossil Diato- 
maceae, and I may add that Ehrenberg, who is preparing to 
publish a great work on this part of the subject^ has been 
very much interested in the Mull earth, as being the first he 
had been able to obtain from the Hebrides, and thus filling 
up a great blank in his work. It is not, however, the first 
that has been discovered in the Hebrides, as there is a Diato- 
maceous earth at Raasay, also in the Hebrides. This I have 
not yet examined, but I presume it has been described. 
I beg to offer to the Society a few slides made, as I have 
stated, from a specimen of 6nly middling quality, such as 
alone has been in my possession of late, and also a specimen 
of earth, not yet examined, in its natural state, which may 
possibly turn out good. I have added a portion of prepared 
earth in water, which cannot be cleaned from quartz fragments, 
but certainly contains a good many fine examples of the rare 
and beautiful Pimiularia alpina. 
The subjoined figures are rough sketches of the doubtful 
