MOSSES AND LIVERWORTS. 267 



successively inhabited by the neighbouring vegetation 

 of all subsequent periods, and the remains of the latter 

 occur in the peat. There are in the lower layers, for 

 instance, roots and trunks of Pinus sylvestris, sometimes 

 in great quantity, showing that at that time Pinewoods 

 were the dominant vegetation. Higher up in the peat 

 there is Bog Oak, which is found at first mingled with 

 the Pine, but entirely by itself in the higher levels. 

 Finally in the uppermost layers the remains of the 

 present neighbouring flora may be found. Thus, from 

 the evidence of the peat, we see that the Pine forest, 

 now characteristic of Norway, and probably corre- 

 sponding to the Sylva Caledonica of the Romans, was 

 replaced by Oak forests, which are known from his- 

 torical evidence to have once occupied most of the 

 Scottish lowlands (see Niven). This oak forest has 

 been replaced by plantations of an artificial character, 

 which are now leaving traces of their occupation in the 

 peat. On the Continent, polished-stone implements 

 have been found in part of the Scotch-fir layers, and 

 remains of Roman weapons are of common occurrence 

 in the Bog-oak deposits. Bones of extinct animals, 

 and even of man, seem to be preserved with extra- 

 ordinary little injury in peat. This is on account of 

 the very peculiar character of a peat moss. Being 

 always saturated with moisture, oxygen cannot pene- 

 trate, and neither the ordinary bacteria of putrefaction, 

 nor worms and other animals are able to exist. Hence 

 the progress of decomposition is arrested ; and, instead, 

 humic acids make their appearance, and these are 

 strongly antiseptic. Thus peat is an accumulation of 

 partly decomposed vegetable material. It consists 

 mainly of carbon, and may contain from 1-2 per cent, 

 nitrogen, 0-4 per cent, calcium, but generally has very 



