J. G. Goodchild—Formation of Coal-seams. 313 
entombed in the zones nearer the land; but with vegetable matter 
the case is different. Vegetable matter has a low specific gravity, 
and its ordinary tendency is to float. It is only under certain 
conditions, and after long maceration, that it sinks at all; and even 
in that case such of it as is in a fine state of division is especially 
long in reaching the sea-bed, even where the bottom is quiet and 
comparatively shallow. In the case we are supposed to be reviewing 
some of the vegetable matter that enters the river near its source 
becomes so far water-logged by the time the estuary is reached as to 
subside to the bottom just outside the zone where the sea-bottom is 
affected by the stronger submarine currents. Much more of the 
- vegetable matter remains suspended long enough to be transported 
to a zone on the seaward side of the last referred to. But most of 
what has been here referred to as the deciduous parts of the 
vegetation, the leaves, fronds, the resinous spores and the spore- 
cases, together with the half-decayed parts of the cellular and 
vascular tissues of the plants themselves, remain in suspension so 
long, and subside to the bottom so gradually, that by the time they 
have finally settled, the submarine currents have transported them 
seawards to a zone well outside that attained by any but the very 
finest sediment. 
There must, therefore, be a constant sorting out of the varied 
material brought down by the river, and it must be that which 
remains longest in suspension that is transported farthest from the 
land. In this way accumulations of vegetable matter, pure, and 
unmixed with mineral sediment, must be slowly and quietly 
gathering off the mouths of most of the rivers that traverse 
regions abounding in vegetation. 
It is important to remember that all the while the physical con- 
ditions of land and sea remained unchanged, the deeper water 
deposits, at all events, would continue to be laid down uniformly ; 
so that, if no disturbance of the relative levels of land and sea 
occurred, there would practically be no limit to the quantity of 
vegetable matter that might thus accumulate in the course of time. 
There is another point to be noticed in more detail. The rate at 
which any given vegetable organism will sink depends upon several 
conditions. Its specific gravity is one of the most important; then 
follows the time it has been exposed to maceration ; the velocity 
of the currents affecting it must affect the results materially ; and 
even the form of the vegetable body itself must be taken into account 
as a factor. But the most important factor of all is the power of 
resistance the body presents to the forces that are tending to reduce 
it to the inorganic condition. If it rots quickly when exposed to 
maceration, it will become water-logged after only a short journey, 
and may reach the bottom within the zone of deposition of even the 
coarser sediment. But if it be of a nature to resist the effects of 
maceration for long periods (as the resinous spores, etc., most 
certainly are), then it will be longer in becoming fully saturated 
with water, and may drift in suspension many miles to the seaward 
of the point where its original fellow-travellers came to the ground. 
