KIUKBY — SANDPIPES IN MAGNESUN LIMESTONE OF DURHAM. 329 



0^ THE OCCURRENCE OF "SAND-PIPES" IN THE 

 MAGNESIAN LIMESTONE OF DURHAM. 



By J. W KiEKBY. 



( Gontinued from ]3acje 298.^ 



On examiniiig the interior of tlie pipes, I have invariably fonnd the 

 surface to be more or less decomposed. For abont half an inch — 

 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; d', Gravel ; e, Clay and soil; c. Boulder. 



scrape it away with the finger-nail. This is the case witli all the 

 beds, no matter how they may differ in texture and general 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 



