444 PREHISTORIC EUROPE. 



peat overlying ancient forests is not an isolated phenomenon 

 peculiar to maritime districts, but common to all turbaries 

 throughout the British Islands and Northern Europe, it seems 

 more natural to attribute the presence of the peat in most cases 

 to changed climatic conditions, which, while unfavourable to the 

 growth of arboreal vegetation, greatly nourished the spread of 

 mosses and marsh-plants. To this subject, however, I shall 

 return. The presence of human relics in the marine beds shows 

 that man still lived in Cornwall after the low grounds were 

 submerged. 



4th, During the period of submergence streams continued to 

 carry sand and silt down to the sea, and now and again quanti- 

 ties of vegetable matter were likewise distributed over the beds 

 of the estuaries. Some of this vegetable cUhris may have been 

 derived from the destruction of the old forest -lands which 

 covered the upper reaches of the valleys and the inland districts 

 generally. It seems in every way comparable with the layers of 

 drifted vegetable matter which occur in the Carse-deposits of the 

 Forth. We may suppose that owing to an increased rainfall the 

 streams frequently rose in flood, and, overflowing the low grounds 

 within their reach, swept them bare of their vegetable covering. 

 It is by no means necessary, however, to infer that the sticks, 

 boughs, twigs, etc., which occur locally here and there in the 

 estuarine beds, are in every case the cUhris of trees which were 

 growing in the vicinity of the Cornish coast -line during the 

 period of submergence. The encroachment of the sea, apart 

 from any other cause, must have told upon the flora ; and we 

 can hardly escape from the conclusion that long before the lower 

 forest -bed had been completely overwhelmed the growth of 

 arboreal vegetation must have received a severe check over a 

 wide district in Cornwall. The old forests must in many cases 

 have decayed and given rise to marshes, so that when the streams 

 rose in flood nothing is more likely than that these should sweep 

 seawards such relics of the ancient woods as came within their 

 reach. In this manner whole rafts of matted vegetation might 

 now and again be undermined and floated off en masse. As this 



