in the Neighbourhood of Edinburgh. 253 
been transported into the basins which they have occupied, by 
the sudden or gradual operation of streams or rivers. Some sand- 
stones, as, for instance, certain beds to the east of Dunbar, contain 
marine shells, while the majority of other sandstones inclose nu- 
merous plants, and thus afford mdications rather of lacustrine 
than of marine deposits. 
Argillaceous shale, which, in the limestone quarries of Gilmer- 
ton, is filled with marine shells, and at Burdiehouse contains the 
freshwater unio, represents the mud, or silt, accumulated in the 
beds of ancient rivers, fresh-water lakes, or seas. 
Limestones, as I have urged, may be of two kinds. While 
that of Gilmerton, adjacent to the Burdiehouse quarry, abounds 
in corallines, encrinites, and shells, all evidently marine, these are 
in vain sought for in the other limestone which presents the re- 
mains of fish, apparently inhabiting fresh-water, and of ferns, ly- 
copodiaceous plants, and such aquatic vegetables as flourish most 
among fresh-water lakes and marshes. While the one limestone, 
therefore, is the memorial of a sea, the other limestone indicates. 
some fresh-water river or lake, within which calcareous matter 
was elaborated. 
With regard to coal, most of the seams of this substance have 
resulted from the decay of vegetables which have grown upon the 
very site in which such seams of coal are found. This fact has 
been incontestibly shewn in the Northumberland coal-field, where 
the large roots of Stigmariz have been traced in coal or shale, in- 
dicative of the vegetable mud in which they grew. It has been 
therefore inferred, that many of the plants of coal-fields flourish- 
ed in still and shallow water.—(See Preface to Vol. II. of the 
Fossil Flora of Professor Linpiey and Mr Hurrton.) Some 
species of coal, however, it is supposed, might have been brought 
from a distance in the form of drifted vegetable matter, to which 
origin certain kinds of cannel, or parrot-coal, are referred. But 
the absence of all attrited, or water-worn pebbles within the sub- 
stance of coal, is fatal to this alleged origin. 
