107 
of Edinburgh , Session 1872 - 73 . 
from a tenth to half an inch apart, and on the whole parallel to 
one another. A thin section, made soon after this notice was read, 
proves that these really are the boundary lines of annual woody 
layers, the structure of which is beautifully shown before a common 
lens. Hence the supposed branch is not such, but a longitudinal 
sector of one, or possibly of a trunk. 
All these fossils are covered with a black shining crust of brittle, 
caking coal, from a tenth to a twentieth of an inch in thick- 
ness, easily detached from the surface underneath. This substance, 
when heated, froths up very much, emits much white dense flame, 
cakes firmly, and burns slowly away, leaving only from 3’5 to 4\5 
per-cent, of ash. 
Under this crust the fossils are of a uniform grey colour, like 
our ordinary tertiary limestone. In most of them the fossilising 
material is very tough, and hard enough to strike fire with the 
hammer. No. 6, however, is dark grey, almost black indeed, till it 
is thoroughly dried, and not so hard as the others. It has evidently 
been long soaked in the moist bottom of the quarry. In all the 
mineralising material is essentially the same, and totally dif- 
ferent from that of the containing strata. These are all a ver}' 
pure, compact, fine-grained, extremely hard, siliceous sandstone. 
Witbam has given no fewer than four analyses of bis fossils, but 
they are all either erroneous or incomplete. Silica occurs, not 
uniformly, in rough particles, to all appearance adventitious, and 
amounting to about 05 per-cent only. Alumina is also present to 
about the same amount. But the great mass of fossilising matter 
consists of the carbonates of iron, magnesia, and lime, each in 
notable proportion. The relative proportion of these carbonates 
varies, even in different parts of the same fossil, the average being 
about 60 per-cent, of carbonate of lime, 17 of magnesia, and 14 of 
carbonate of iron in the form of protoxide. The proportion of the 
last ingredient varies most of all, for it sometimes rises so high 
as 28. The most interesting ingredient, however, is carbonaceous 
matter, which is always left after the solvent action of acids, in a 
proportion varying from 2*75 to 9-0 per-cent, and in a state of 
extremely fine division. This is not coal, like the external crust, 
but charcoal, burning away with a red glow, and no flame, and 
apparently not possessing the properties of graphitic charcoal. It 
