168 A. J. Julces-Broicne^-The Vale of Marshwood. 



axis of the pericline, and the streams run both northward and south- 

 ward, so that both lines of escarpment are trenched by river-valleys. 

 In the case of the Dorsetshire Weald the original watershed was 

 outside and north of the central axis, so that all the streams ran 

 southward and only the southern border is trenched by river-valleys. 



In both areas, too, the denudation of the central region has laid 

 bare a large tract of clay, and on this clay-soil fine forests of oak- 

 trees came into existence. The great forests of the Weald were 

 famous for their oaks, which in former days contributed largely to 

 the " wooden walls of England." In the western country the Yale 

 of Marshwood was equally celebrated for its oak-trees, and when 

 ships were largely built in the South of England they were much in 

 demand. Many hundreds of fine oak trunks have been taken from 

 the Vale and shipped from Lyme and Bridport. The trade indeed 

 has not entirely ceased, and such cargoes are still embarked at the 

 small port of West Bay, below Bridport ; few, however, now come 

 from the Vale of Marshwood, for its woods have disappeared, and 

 the only oaks that remain are hedgerow-trees. 



With respect to the isolation of Filsdon and Lewesdon Hills, 

 this has been effected by the excavation of the intervening spaces ; 

 in technical language they are "hills of circum-denudation." The 

 interspaces are the heads of the valleys formed by the action of rain 

 and springs on the slopes of the old watershed. The tributaries of 

 the Axe have trenched it on the north, while on the south side the 

 strong springs thrown out at the base of the Marlstone Sands have 

 eaten backward some little way into the ridge of the original water- 

 shed, causing the actual water-parting to retreat northward. This 

 recession has taken place principally near the villages of Pilsdon 

 and Bettiscombe, while Lewesdon may really be very nearly on the 

 site of the original ridge of the watershed. 



The same process has taken place near Beaminster, where the 

 spring-heads which furnish the headwaters of the Brit have un- 

 doubtedly eaten deep into the Chalk and Greensand area, and there 

 tlie escarpment is still receding, as the frequent scars of landslips 

 testify. 



It will be seen, therefore, that the history of the evolution of the 

 present physical features of West Dorset involves the consideration 

 of many agencies and many conditional phases. Here, as elsewhere, 

 rain, rivers, snow, frost, and heat have been the principal agents at 

 work, but in order to understand how their operation has resulted in 

 the particular arrangement of hills and valleys which we see around 

 us, we must form some conception of the conditions under which 

 they started to work, and we must remember that their working 

 powers have always been guided and modified by the changes in the 

 relative height of sea and land, those slow movements of upheaval 

 and subsidence to which every portion of the earth's crust has been 

 repeatedly subjected. 



