360 Proceedings of the Royal Physical Society. 
some of the preserving salts of Nature, probably silica in this 
instance, and would be made immortal by being petrified, 
and by having its structure as perfectly preserved as when 
it flourished in the forests of its time. It sometimes 
happened that some parts of the pieces of drift-wood 
putrified, as it were, and the structure was destroyed and 
the substance of the wood left in an amorphous state, as 
seen in the scurf of parrot-coal adhering to the outside of 
the specimens. The tree of which these sections were once 
parts is now, after a few aliases, known to fossil botanists by 
the name of Araucaroxylon Witham, and is considered to have 
been one of the stateliest monarchs of the woods of that time, 
as witness the fossil trees of Craigleith, described by Sir Robert 
Christison and others, good boles of which may be seen in front 
of the Museum of Science and Art in Chambers Street, and 
in front of the Herbarium, Royal Botanic Garden, Edinburgh. 
It also may be interesting to detail roughly the strata 
exposed in the Baberton New Quarry. The main bed is the 
coarse sandstone, with its numerous impressions of drift- 
wood, about 20 feet or so in thickness; then a thin layer, 
only a few inches deep, of fire-clay, topped by a shallow seam 
of coal, perhaps not more than an inch in thickness; then 
6 or 8 feet of coarsely coherent shale, in which thin layers of 
sandstone occur; then a bed of coarse-grained sandstone. 
As fire-clays are now generally considered to have been old 
soils and coals (the remains of the vegetation that grew in 
or upon them), we have here evidence of a land-lake in 
which the great bed of sandstone and drift-wood was de- 
posited till it was silted up and converted into dry land or 
perhaps marsh land, and capable of bearing a vegetation 
peculiar to its time or condition, and that afterwards 
it was again converted into a lake as before, but without the 
great amount of drift-wood that so emphatically characterises 
the older lake. This change is, we think, amply proved by 
the occurrence in the fire-clay of Lycopod -spores, the cast- 
away seeds of the trees whose substance formed the coal, 
and further, by the frequent occurrence of Stigmaria roots 
in the fire-clay and in the silt of the second lake. 
The general condition m which fossil wood is found varies 
