RECENTLY DISCOVERED IN CRAIGLEITH QUARRY. 219 
internal structure had been loosely cellular, both of these lepidodendrons were 
casts merely, the whole interior consisting of the same material as the matrix, 
and without traces of vegetable tissue. 
The sandstone of Granton, when worked for the harbour and adjacent 
houses, was considered to be of the same quality as that of Craigleith. That 
opinion is borne out by the properties of the large rectangular blocks, from two 
to three tons in weight, very many of which have lain unused, east of the quarry, 
since it was flooded in 1855. Most of them present the characters of the 
Craigleith “liver” rock; but many, too, are now yellow outside, possess all the 
other external properties of the ‘‘ bastard whin,” effervesce with acids, and yield 
to them largely lime, magnesia, and oxide of iron. 
Conc.Lusions.—The trees found in the fossilised condition in the quarries of 
Craigleith and Granton must have been water-borne, and by a tumultuous 
flood, for they have all been entirely stripped of branches, roots, and bark. 
They may have arrived at their present site either with the sand, which finally 
formed their hard sandstone bed, or subsequently, while it was a quicksand, 
through which they could easily sink, their heavier root-end foremost. 
The sand in the course of time passed into the state of sandstone, for the 
most part by the simple accretion of particles through the long-continued influ- 
ence of pressure and crystallising force. But in some places accretion has been 
aided by agglutination with carbonates conveyed among the particles by solu- 
tion in water. 
The trees, after arriving in their bed, had been fossilised by a peculiar 
process. It appears that acrogenous stems, lying in the same matrix, had been 
fossilised simply by the sandy particles invading their loose open cellular texture 
as it decayed, and subsequently accreting like the sand around them, so that 
interior structure is not preserved. But the compact, fine-grained wood of the 
_araucarious trees could not be so penetrated. Fossilisation has been effected in 
them by a different, probably much slower method,—by long infiltration with 
water holding in solution carbonates of lime, magnesia, and protoxide of iron. 
It is by no means easy to seize the whole details of this fossilising process. 
But the theory which occurs to me as accounting best for all the facts, is that 
of a process at ordinary temperatures of very slow destructive distillation, which 
bears, to the well-known. process of destructive distillation of wood at a red 
heat, the same relation which Ligsia’s process of eremacausis, or slow natural 
oxidation in the atmosphere, bears to ordinary atmospheric combustion, In 
both cases of destructive distillation bituminous matter is discharged, and char- 
coal left behind. In both cases the woody structure is preserved. In the 
fossilising process the charcoal is squeezed up against the cell-walls by the 
VOL. XXVII. PART II, 3 L 

