PROCEEDINGS OF THE COTTESWOLD CLUB 85 



water, the additions received to the surface supply by 

 springs, and the seasons of maximum and minimum and 

 mean flow, are all influenced by the nature of the rocks 

 over which the water flows, the character of the country 

 where the river takes its rise, and the physical features of 

 the surface along its course. 



Of all these conditions, the permeability of the rock, 

 whether due to a soft or spongy and porous nature, 

 or to the presence of numerous fissures into which 

 water freely passes is necessarily the most influential. In 

 absorbent rocks it rarely happens that under heavy rainfall, 

 in a wet season the pores do not become choked, and the 

 absorbency checked ; but in fissured and cavernous rocks 

 communicating with the interior by large crevices, which 

 condition is so common in the tumbled and broken Lower 

 Oolitic Rocks of the Cotteswolds there is practically 

 no limit. 



The waters in the several Catchment basins where they 

 traverse the Great Oolite often lose much of their surface 

 character, as developed by the Fuller's Earth, passing 

 down out of sight into absorbent beds in the Great 

 Oolite. They become imprisoned until arrested by faults, 

 in which case they ascend as Artesian springs, overflow- 

 ing into the surface channels. Such peculiarity is con- 

 spicuous in the Churn, which after passing over the 

 impervious Upper Lias for nearly 6 miles from its source, 

 (the Seven Wells) attains a volume of from 300 to 400 

 cubic feet per minute. Six miles lower down, after tra- 

 versing the porous beds and fractured freestones of the 

 Inferior and Great Oolite, near Cirencester, the volume 

 diminished to 30 cubic feet per minute, or 270,000 gallons 

 per day. The lost surface water, however, was still under 

 the Valley of the Churn at the depth of 91 ft. O in., as 

 determined by Mr Taunton in 1872, and forcibly ascended 

 through the bore and overflowed. These facts cannot be 

 overlooked where faulted ground, in some cases, so 



