Jd. G. Goodchild—Formation of Coal-seams. - ‘3éll 
In rarer cases still the change can be traced through this last into 
impure limestone. Of this more presently. 
Sedimentary formations of nearly every geological period contain 
coal-seams in one part of the earth’s surface or another; and under 
every variety of geological or of geographical circumstances they 
present much the same features; and—allowance being made for the 
changes the containing rock may have undergone—their composition 
also is in nearly all cases practically constant. It would seem, 
therefore, that the formation of coal does not require any very 
exceptional conditions, such as an excess of carbonic acid in the 
atmosphere, or other abnormalities. 
There is often a curious (and significant) relation between the 
nature of the rocks associated with coal and that of the vegetable 
“matter entombed therein. In the Carboniferous series proper the 
sedimentary strata associated with the coals are usually shales; 
fireclays, and beds of sandstone of various degrees of coarseness 
also occur. In certain areas limestones and calcareo-siliceous beds 
(‘“‘cherts”) are also found. Vegetable. remains commonly occur 
dispersed throughout all of these, though the proportion varies 
much with the nature of the rock. It is in the coarse, drifted, 
material forming the sandstones, that tree trunks, if they occur at 
all, are most commonly found. And it is here that they are so often 
found embedded stem upward and root downward, reminding one so 
forcibly of the “snags” that are common in the sandy deposits of 
tropical rivers. (It should be noted, in passing, that the centre of 
gravity of most of the trees of the Carboniferous period must have 
lain close above the roots; so that in floating, they must have 
travelled root downwards, and as the decay of the soft interior 
proceeded, they must have tended invariably to sink to the bottom 
in nearly the position of growth.) The shales associated with coals 
rarely contain trees (I have not come across any proof that they ever 
do so); but fronds and leaves occur in plenty, and, more rarely, 
stems and small boughs may occur as well. ‘The fireclays (which 
are commonly regarded as old soils that have been exhausted of their 
alkalies and iron by the growth thereon of vegetation) often, but by 
no means invariably, contain roots—the well-known Stigmaria—in 
addition to the vegetable constituents found in the shales. Some 
sandstones show these Stigmaria roots as well, whether the rock is 
directly associated with coal or not. If limestones occur with the 
coals, these rarely contain traces of coal, except as lenticular masses, 
which are clearly due to the entombment of vegetable matter that 
has been drifted. A fine and well-known example of this kind is 
seen in the Mountain Limestone of Ingleton in North Yorkshire. 
A careful consideration of these facts relating to coal will make it 
clear that, whatever be its precise mode of origin in any given case, 
coal presents all the characters of a stratified deposit. It resembles 
most closely, in many of its characters, those strata that have slowly 
and quietly accumulated in nearly-still water. The resemblance to 
a stratified deposit is certainly not delusive and to be attributed to 
the effect of subsequent compression, because, as we have seen, the 
