^"ounSi, ocr^iT^^^^^^ -^^2/^^ Microscopical Society. 179 
insufficient to isolate ttie bed or has had in itself iron or lime, some 
of which it has parted with, that nodules are found in the coal, 
making the seam where they occur in quantity of less economic 
value, but supplying to the naturalist the means to some extent of 
reading the life history of that period. By the mysterious power 
of selection and accretion which has formed nodules in sedimentary 
rocks, fragments of the tissue of the bed have been arrested in their 
decay, and converted into imperishable limestone. It is seldom that 
the preserving material has had access to the structures in time to 
preserve them in their entirety. The more delicate cellular tissue has 
generally been completely lost. The Arran specimens are remark- 
able exceptions to this state of things, and this is probably owing 
to the conditions under which they were buried. The hot ashes, 
which formed their tomb, appear to have completely charred them, 
and then, converted into charcoal, they resisted decay and pressure 
until every cell and cavity was filled by the infiltrated carbonate of 
lime which converted the loose ashes into a compact stone, and 
at the same time made permanent in its original form all the most 
delicate structure of the plant. 
The specimen I select first for description is one from the 
cabinet of Dr. Millar, belonging to the type described by Mr. Binney 
under the name Sigillaria vascularis* As the specimen belongs to 
Lepidodendron selaginoides, Sternb., I shall employ, in accordance 
with the invariable practice of naturalists, the older name in speak- 
ing of it. I have chosen this species because it is one that may 
easily be obtained by students. I have it from difi'erent localities, 
and Mr. Binney tells us that the Halifax Hard Seam or Granister 
coal at South Ouram, near Halifax, contains in some places so 
many of the nodules as to render it useless — that they occur over 
a space of several acres, then almost disappear, but occur again as 
numerous as before, — and that this has been traced over a distance 
of twenty-five to thirty miles. 
As the technical terms which I shall be obliged to use for per- 
spicuity are somewhat difierent from those employed by Mr. Binney, 
there is the more necessity for redescribing this fossil; besides, I 
shall add some points which I have determined in my examination 
of the series of specimens which have passed through my hands. 
The stem of the Lepidodendron selaginoides, portions of which 
I have figured on the Plate, is somewhat compressed, being 1 inch 
across its greater diameter and f of an inch across its lesser. 
The axis of the stem is composed of scalariform vessels of large 
diameter. In transverse section (Fig. 1 a) it is seen to be composed 
of two parts — 1st, a central portion, consisting of vessels of difierent 
* " On some Fossil Plants showing Structure, from the Lower Coal-measures 
of Lancashire," by E. W. Binney, Esq., F.R.S. ' Quart. Journ. Geol. Soc.,' vol. 
xviii., p. 106, PI. IV. and V. The stems described under the same name in the 
' Phil. Trans.,' by Mr. Binney, are different, and are consequently not taken into 
account in the present notice. 
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