5^ 
Dr MacCulloch on Peat 
which the vegetation of these soils is exchanged for more profit- 
able plants. To these must be added the growth of larch, un- 
der which the original covering is gradually extirpated, and re- 
placed by a green and grassy surface, applicable to the pasturage 
of cattle. 
Although the formation of marsh-peat ceases, when, from 
the gradual increase of elevation, or from other causes, the bog 
becomes drained, this substance still continues to be generated, 
but in a slowet manner, by the plants that form it on mountain- 
declivities. 
The formation of forest-peat must be considered to have ter- 
minated with the decomposition of the wood which has first 
fallen, although the process still goes on in a different manner, 
by the growth and decay of the various plants which occupy 
the same place. A few cases are however known, where it ap- 
pears that forests have successively grown and fallen on the same 
spot, so as to have continued the original process. 
The peat of lakes is necessarily completed, when once the 
water has disappeared ; and in a similar manner, that which is 
formed from maritime plants, ceases to grow, when, by the final 
exclusion of the sea, the character of the vegetation is changed. 
Of the formation of transported peat there is no end, as long 
as the flow of water from mosses continues, and cavities exist in 
which the material can be deposited. 
As the increase of peat necessarily keeps pace with the growth 
of the plants from which it is formed, it is evident, that the ces- 
sation of the one is implied in that of the other, with the excep- 
tion of transported peat, which does not directly depend on the 
Same cause. That it may be renovated after cutting, it is there- 
fore necessary that the process of vegetation be renewed where 
it has thus been suspended. In mountain-peat, it has already 
been shewn that this takes place naturally, as this variety gene- 
rally approaches so much towards ordinary vegetable soil, as 
readily to admit of the lodgment and growth of seeds. But the 
compact and perfect varieties which are exposed by the opera- 
tion of cutting, are not thus susceptible of renewed vegetation, 
as no plant seems willingly to attach itself to peat in this state. 
But if the pit has been so formed as to admit of the stagnation 
of water, the process is sometimes renewed by the same series 
