KIRKBY — SANDPIPES IN MAGNESIAN LIMESTONE OF DURHAM. 331 
where the pipes are very numerous, tlie limestone is more of a slaty 
nature, though tliicker bods of a crystalline and concretionary 
character are associated. Some of the beds are finely laminated, and 
a few are soft and marly. 
Some of the pijjcs begin in rubble overlying the solid beds on the 
south-west of the quarry, and a few small ones about two feet in 
length are solely excavated in it. The rubble only exists in this 
region, where the uppermost beds of limestone seem to have been 
completely broken up, and all signs of their stratification destroyed, 
by a disturbance of which further traces are still visible in a broken 
syncline a little beyond the most westerly pipes. The pijies shown 
Lign. 6. — Section of Pipes in Rubble, near the Slope of a Syncline. 
e. Sand, clay, aud soil (the sand thinning out here) ; ij. Thin bedded limestone, much fissured 
and broken to tho west ; g', rubble. 
in fig. G, which are close to the syncline, are altogether in rubble. 
The form of the pipes in such loose materials seem to be just as well 
preserved as when the substance pierced is unbroken. 
These are about all the facts that it seems necessary to notice in 
describing the pipes ; and so much has been said on the origin of 
sand- and gravel-pipes by the various authors who have studied and 
written on those in the chalk, and being perfectly satisfied that those 
in the magnesian limestone have been similarly originated, that it is 
scarcely necessary for me to go far into the question, though it may, 
perhaps, be necessary to draw attention to the theories broached, and 
