Dr MacCulloch on Peat 
original peat becomes buried to a considerable depth, and as 
such plains are generally brought into cultivation, it is never 
again renewed. Alternations or deposits of marl are only found 
in those situations where the peat has been generated in a lake ; 
and they offer a criterion, not only of the former existence of 
lakes which have long since disappeared, but are capable of de- 
termining, to a certain degree, the depth which these once pos- 
sessed. 
Mountain peat is not limited strictly to mountainous declivi- 
ties, but is found in all situations where the drainage is consider- 
able. This variety is commonly loose in texture, and its average 
thickness may be estimated at a foot. It rarely amounts to two 
feet, and often does not exceed as many inches. As an article 
of fuel it is of little value, when compared to the other varieties, 
from its thinness and want of compactness ; but it is more inte- 
resting in an agricultural view, from the great extent of surface 
which it occupies in Scotland, and from the comparative facility 
with which, in low situations, it is brought into cultivation. The 
dry moor lands are generally covered with this variety, or with 
a variety intermediate between it and the more compact peat of 
marshy and ill drained situations. The plants which principal- 
ly conduce to the formation of mountain peat are the follow- 
ing : 
Erica cinerea. 
vulgaris, 
tetralix, 
Myrica gale. 
Empetrum nigrum. 
Tormentilla erecta. 
Arbutus uva ursi. 
Vaccinium vitis idaea. 
Juniperus communis. 
Marsh peat is chiefly formed in flat undrained lands, or on 
the margins of lakes, while it is also produced during the last 
stage of the formation of lake peat, with which it is therefore 
often found united, constituting the upper surface of the more 
compact variety which has been generated under the water. It 
is often found occupying extensive plains, and presents a great 
variety of aspect. These varieties depend chiefly on the very 
various state of drainage, arising either from situation, or from 
difference of season ; and as such extensive plains often retain 
Polytrichum commune. 
Lycopodium clavatum. 
Lichen rangiferinus. 
Nardus stricta. 
Scirpus caspitosus. 
Juncus squarrosus, together 
with various grasses, chief- 
ly belonging to the genera 
Aira, Agrostis, and Carex. 
