,72 DRINKING POOLS. 7, 



they would have rlfen to the furface, and 

 have left the clay wholly cxpofed at the bot- 

 tom : even flones themfeives lie in water vi^ith 

 little more than half their weight in air. 



This propenfity in the covering materials, 

 when covered with water, to rife towards the 

 furface, and- the fl;aie of fofrnefs which the 

 clay is rtduced to by a free communication 

 with the water, render them very liable to be 

 di'durbcd by the feet of cattle ; thus expofing 

 the clay to injury from above : while lubtcr- 

 rancous water, after heavy rains, iiiay infl- 

 iniatc itfelf beneath the clay, and not only 

 diliurb the lime, but raife up the clay, and 

 affill: in rendering the coatings Hill lefs firm ; 

 or, in other words, in promoting the general 

 tendency of the whole to form an artificial 

 quagmire. 



But if a pond were properly paved while 

 the coats were yet in a firm folid flate j the 

 pavement, beirg an inverted dome and adl- 

 Ing as an arcb againft their upward ten, 

 dency, would prcferve them in that ftate fo 

 long as the arch itfelf Ihculd remain per- 

 fect ; which muiL of nccefTity be until the 

 ^ones were worn out, or the foundation on 

 '(Vhich they relied fliould give way. For the 



prcfTure 



