118 Br Fleming’s Remarks on the Modern, Strata. 
operating in their production, act so frequently in concert, that 
it is not easy to assign to each its due share. All of them are 
subject to considerable irregularities^ occasionally suspending 
their influence, or renewing their operations with redoubled 
violence. But the situations of these different strata, and the 
classes or orders into which they may be distributed, will be 
better understood by the following remarks. 
1. SolL — The varying conditions of the atmosphere, in refe- 
rence to temperature and humidity, exercise a powerful influ- 
ence on the inorganic substances exposed to their disintegrating 
and decomposing effects. A film of earth is produced fit for the 
support and the nourishment of vegetables, which speedily clothe 
the surface. The history of the soil (in reference to its compo- 
sition and structure), now under the influence of vegetation, 
must be studied in connection with the physical and geographi- 
cal distribution of plants. The increase of the quantity of car- 
bonaceous matter, marks the number of plants which have 
flourished and perished. Extensive forests are established in 
certain districts, and for ages, by the annual falling of their 
leaves, increase the thickness of the stratum by which they are 
supported. But this addition to its thickness seems, in some 
cases, to impair its fertility. The trees decay, mosses and li- 
chens multiply, and the soil, instead of supporting any longer a 
forest, receives an addition of a layer of peat. But, in some dis- 
tricts the peat has been formed, in the absence of a previously ex- 
isting forest, by the growth of the mosses and lichens alone. In 
-Zetland, I have observed peat ten feet in thickness, consisting 
of the relics of that common moss Trichostomum lanuginosum., 
which continues to flourish vigorously on the decaying remains of 
its progenitors, or of itself. There is one difference, however, 
prevailing between the forest-peat and the moss-peat^ deserving 
of notice. The soil under the former is always of some thick- 
ness, — while under the latter it, in many cases, can scarcely be 
said to exist. Partial depositions of bog-iron ore and marl occur 
in this formation. The marl usually consists of fluviatile shells, 
or encrusted masses, and its origin may be traced to springs 
holding carbonate of lime in solution. 
2. Sand-drift, — The products of the disintegration of inor- 
'ganic matter, from whatever cause, — the action of the atmos- 
