KIRKBY — SANDPIPES IN MAGNESIAN IJMESTONK OF DURHAM. 329 
ON THE OCCURRENCE OF "SAND-PIPES" IN THE 
MAGNESIAN LIMESTONE OF DURHAM. 
By J. W KiRKBY. 
(Continued from page 
On examining the interior of the pipes, I have invariably found the 
surface to be more or less decomjoosed. For about half an inc4i — 
sometimes less and sometimes more — the texture and hardness of the 
limestone is completely changed — so much so that it is possible to 
Lign. 4.— Section of Oblique Sand-pipes on South Side of Quarry. 
d. Sand; Gravel ; e. Clay and soil ; c, Boulder. 
scrape it away with the finger-nail. This is the case with all the 
beds, no matter how they may differ in texture and genci'al character, 
though some seem more affected than others. This alteration is best 
seen in those strata that are crystalline. In one part of the quarry 
VOL. III. 2 T 
