NOTES AND QUERIES. 
261 
dapressions gradually iacreasing in size by the continuous action of the acidu- 
lated water, would grow in proportion to the activity or duration of the srrosive 
action. This action would also be exerted in equal portions round th3 cir- 
cumference of the hoUow, provided that the sands or gravel above were of a 
moderately uniform texture, and its result would be to give the pipes a more 
or less circular, funnel-shaped, or cylindrical form, depending greatly on the 
solidity of the chalk and the duration of the errosive agent in action. The 
longer this action continued, the greater would be the tendency to deepen 
vertically, or in other words, to pass successively from the "cup" to the 
" funnel-shape" (fig, 3), and lastly to the cylindrical form presented in the 
diagram (fig. 1). 
Mr. Prestwich explains the gradual formation of these pipes in the following 
manner : — 
Fig. 5.— Horizontal section of sandpipe. 1 Fig. 6.— Vertical section of one in course of 
1 formation. 
P 
Fig. 7.— Vertical section in a more advanced state, showing where the action ceaeee, 
except in a vertical direction towards "P." 
" If we divide a line drawn through the centre of the horizontal section of 
the top of a pipe into three equal parts {A a, a b, b fig. 5), and carry 
down two perpendicular lines from a and b until they meet the sices of the 
pipe at c and d in the vertical sections (figs. 2 and 3), it is evident that in 
(fig. 2) the relative dimensions oi Ac, c d, and d B, are very nearly the same, 
the line c d being very little less than c A or d B ; still the difference is suffi- 
cient supposing equal quantities of water to pass in equal time through the 
equal widths A a, a b, b B, to make the relative quantity supplied to c d 
greater than that supplied to Ac and B d ; consequently in (fig. 3) the water- 
wear between c d would be slightly greater (aided also by the tendency of the 
water to converge at p) than between A c and B d, and t!ie cavity of the incipient 
