II 



THE UPPER THAMES VALLEY 



FROM the Vale of Pewsey our road struck northward 

 over the Marlborough Downs, where the soils are 

 deeper and heavier than on Salisbury Plain. On this 

 northern section there are more indications of the 

 formations which once covered the chalk but have 

 been destroyed without being quite denuded away, 

 until there remains on the surface something approxi- 

 mating to the red Clay-with-Flints of the North 

 Downs and Herefordshire. Another sign is the 

 presence of the Sarsen Stones or Grey Wethers, huge 

 blocks of fine-grained sandstone which lie like giant 

 flocks about the grassland of the Marlborough Downs, 

 though too often they have been broken up for building 

 and road-making, gate-posts, and the like. They are 

 supposed to be indurated cores from the Tertiary 

 Sandstones which once lay above the chalk and have 

 disappeared in the making of the Clay-with-Flints. 



From Marlborough the Ogbourn valley allows of 

 an easy passage northwards until, a few miles short 

 of Swindon, the chalk terminates in an escarpment 

 looking over the broad vale formed by the Oxford 

 Clay and constituting the western end of the Vale of 

 the White Horse, through which winds a well-nigh 

 derelict canal joining the Stroud Canal with the 



Thames at Abingdon, and running almost parallel with 



163 



