KIRKBr — SANDPIPES IN MAGNE3IAN LIMESTONE OP DURHAM. 297 



The pipes are found in the limestone beneath the sand beds. 

 I have never noticed them where the sand is absent ; and thongh 

 they are sometimes filled with clay, or a mixture of clay and sand, 

 yet in these instances a thin layer of sand is always the immediate 

 cover of the limestone. Nevertheless, the quarrymen assert that 

 pipes have occurred in other parts of the hill where the limestone is 

 immediately covered by the boulder-clay. They do not occur 

 towards the higher portion of the slope where the gravel is piled 

 against the face of the limestone ; nor further up where the lime- 

 stone is merely covered with turf ; nor have they as yet been noticed 

 in any other locality of the magnesian limestone. 



Lign. 3. — Sand- and Clay-pipes on North Side of Quarry, the Alluvium removed. 



a a. Pipes filled with sand ; h h. Pipes filled with clay ; g g, Thick -bedded, crystalline, and 

 concretionary Limestone. Some of the pipes in. this' figure do not show their true 

 terminations. 



The general form of the majority of the pipes is tubular (figs. 

 1 and 2), but often irregularly so ; some few are conical, but such are 

 usually of slight depth ; others seem to be modifications of these 

 forms ; occasionally they are almost flask-shaped (fig. 3), and in some 

 instances, by the coalescence of two pipes, they appear to be bifid. 



The depth of the longest is about twelve feet, but in one case the 

 termination was not reached at this depth. The depth of the 

 majority is within six feet ; but there are pipes of all depths from 

 one foot to twelve. 



Generally their width is proportionate to their depth, though in 

 this they do not observe much uniformity. It is curious to observe the 

 irregularity of width of some, especially of those I have termed flask- 

 shaped. Such pipes are of less width a foot or two below their 

 apertures than towards each extremity, the lower portion of the 

 tube being the most capacious. In some pipes I have noticed a 



VOL. III. 2 P 



