WELLS AND WELL SINKING. 31 



cavation thus proceeds inside the curb, which will 

 be supported by the props as shown and the process 



FIG. 9. 



repeated. The props are inclined and spiked to 



the upper curb and rest on sole plates. Great 



care must be taken when the brickwork rises to 



the underside of the second curb in order to fill up 



the space very fully between the 



two sections with cement. It 



will very often occur when the 



bricks are laid as in fig. 8 that 



the earth will swell and bind 



them together, in which case the 



curb would be dispensed with, 



and bricks being added under FIG. I0 - 



the executed steining. For a 9 in. lining, laid as 



headers and stretchers as shown by fig. 10, the curb 



system is the best. In passing it may be said that 



