KIRKBY — SANDPIPES IN MAGNESIAN LIMESTONE OP DUEHAM. 295 



new theory of tlie origin of sand-pipes, but because it is well that the 

 occurrence of such as are found in other calcareous rocks than chalk 

 should be recorded, and especially when in rocks which differ from 

 the latter in general structure and greater hardness. 



The tubular cayities or pipes, that I am about to notice occur in a 

 new quarry belonging to Sir Hedworth Williamson, which has been 

 lately opened on the northern slope of an eminence of the magnesian 

 limestone called Fulwell Hill, and which is about a mile and a-half 

 north of Sunderland. The summit of the hill is about two hundred and 

 thirty feet above the sea, but the site of the pipes is only about one 

 hundred and fifty feet above that level. The limestone of this hill 

 belongs to the upper portion of the magnesian limestone series, being 

 the upper limestone of Howse, and the crystalline, earthy, and com- 

 pact limestone of King. This eminence, like most of the surround- 

 ing country, is covered more or less with boulder-clay, the covering 

 being comparatively thin on the top, but of greater and increasing 

 thickness on the slopes and lower levels. 



On the northern slope of the hill, and at the site of the pipes, the 

 boulder-clay has been removed, and in its place are beds of sand, and 

 clay without boulders, with some shingle and gravel. The limestone 

 surface is also worn here, and has every appearance of having once 

 occupied a position between tide marks — at least, it has the appear- 

 ance of having been subjected to the action of water. But to pro- 

 perly understand the relation of these beds to the limestone surface, and 

 to the pipes in the latter, I refer to the accompanying woodcut (fig. 1), 

 which gives a transverse section of the deposits i am describing. 



The contour of the general surface is given by the line a a, and the 

 worn surface of the limestone by h Id, which at h' takes the form of a 

 low terraced cliff, the ledges being smoothly rounded, and in some 

 places rather hollowed out beneath. Against the face of this cliff is 

 piled an irregular mass of gravel and shingle, the pebbles being 

 chiefly from the magnesian limestone, with others derived from the 

 boulder- clay, some of the former being sub-angular. Very little 

 order is to be observed in the arrangement of the gravel, it being 

 heaped against the rock just as we sometimes see gravel thrown 

 against the base of a cliff on recent coasts : some of the pebbles are 

 coated with calc sinter. Immediately upon the surface of the lime- 

 stone, and occasionally in slight hollows of it, are large boulders, c c, 

 of mountain limestone, basalt, and other rocks, which are most 

 undoubtedly the heavier boulders of the boulder-clay originally cover- 

 ing this surface, the greater weight of which has enabled them to 

 withstand the denudative forces which removed the rest of that 

 deposit from this area*. Upon the surface of the limestone, and 



* This is the case where the drift, or boulder clay, is now being denuded on 

 the Durham coast. I know of several instances of the kind in the neighbour- 

 hood of Sunderland, one of the best occurring about two miles or more to the 

 north of the harbour, on a level tongue of limestone called Whitbm-n Steel. 

 Scattered over its surface are some dozens of large boulders of mountain-lime- 

 stone, magnesiaii-limestone, millstone -grit, and basalt, the majority being par- 



