Paleophytology. — 425 
hence developed on it, fed by the abundance of food-material which it 
contains. As soon as it becomes firmer, trees and shrubs, willows, 
alders, and buckthorns, spring up on it, and finally also conifers ; but 
the life of these larger plants is as a rule somewhat limited ; and when 
they are blown down by the wind or fall by their own weight, the peat- 
moss grows over them, and in the course of years they become entirely 
-coyered up by it. There, excluded from the action of the air, they do 
not decay, the structure of their wood being retained perfectly for cen- 
turies. This is the mode in which peat is formed. 
_ Even in lignite the remains of plants can be abundantly recognised. 
‘This is less the case in true coal, and scarcely at all in anthracite, the 
hardest coal with most of a mineral character. It is often possible to 
determine the’plants which have contributed to the formation of coal 
only from the fossils and impressions found in the accompanying beds 
of earth. The exclusion of the atmosphere, and the pressure, often 
immense, which beds of peat that have been flooded and buried 
beneath the surface have had to sustain from the superincumbent 
layers of earth, explain their transformation, first into lignite and then 
into true coal. In many beds of coal, as for instance those of Silesia, 
. their origin from layers of peat is sufficiently evident ; in others this 
explanation does not seem to apply, and we must assume that drift- 
wood has been the source from which they were formed. Even at the 
present time the gigantic rivers of America tear down from their banks 
and carry away trunks of large trees ; and when these trunks have 
become completely saturated by water, they are left behind by the 
current, and sink either in an inland lake, at the mouth of the river, as 
‘in the Mississippi, or in the sea as drift-wood, and thus form immense de- 
posits which may very easily be transformed into coal. But these trunks, 
must retain some traces of their journeyings, and must be intermixed 
with the remains of water-animals, and, when the deposition takes 
place in the sea, of marine plants. These phenomena are in fact ob-— 
served in many of the coal-formations of north Germany, the produc- 
tion of coal having taken place in the manner already indicated. The 
formation of coal from the deposition of successive layers of plants in 
primeval forests is very improbable. 
It is remarkabie that after the Carboniferous period the 
luxuriance of vegetation appears to have diminished. As if 
the earth were already exhausted, one form after another 
of the existing vegetation disappears ; and in the Permian 
sa series, Oniy the lower strata, the Mew Red Sandstone, 
