110 The Heath Formation 



The bracken fern (Pteris aquilina) is rarely common 

 away from the stream-sides, where it is generally as- 

 sociated with trees, and very likely marks the relics of 

 degenerated woodland. 



Pinus sylvestris apparently owes its prevalence on 

 some of the New Forest heaths to its introduction into 

 Ocknell Clump in 1776, though there is some evidence of 

 its much earlier occurrence in the district. It flourishes 

 exceedingly on the poor soils, and sows itself freely on 

 the unenclosed heaths. The natural afforestation of the 

 heathland by the pine is however often checked, just as it 

 is on the Bagshot sand and plateau gravels of the London 

 basin, by the frequent forest fires set alight by careless 

 or mischievous passers (see p. 117). 



5. Western heaths. On the Devonian sandstones and 

 grits of Bxmoor and on the granite of Dartmoor extensive 

 heaths are developed, but in both regions local patches of 

 the true moor formation occur on deep peat. 



Of the Cornish heaths those of the Lizard peninsula 

 are interesting because of the occurrence of Erica vagans, 

 the so-called "Cornish heath," a plant of south-west 

 Europe which occurs nowhere else in the British Isles. 

 It is dominant over large areas of the Lizard heaths in 

 association with the common species — Calluna vulgaris, 

 Erica cinerea and occasionally E. Tetralix. The vegetation 

 of these heaths is not otherwise remarkable. Ulex Gallii 

 is abundant and forms a beautiful feature, as on most of 

 the western heaths. The abundance of Schoenus nigricans, 

 which is very local further east, is also striking. Most of 

 the species of south-west Baropean plants for which the 

 Lizard district is famous occur on the grassland of the sea 

 cliffs or in their clefts, and not on the heaths. 



Erica ciliaris is also found in several localities in 

 Cornwall, though not in the Lizard peninsula. As in 

 Dorsetshire it generally occurs as a member of the 

 wet-heath association. 



