E. Greenly — Sandstone Pipes. 23 



bottom is not seen, gives rise to a shallow cave, and in this it 

 appears to widen out somewhat behind the face of the crag, as 

 though it were there more basin-shaped than where cut by the plane 

 of section. The bedding of the sandstone in the pipe is somewhat 

 irregular, and bends gently downwards near the mouth. 



The material of the plugs is a fine white, hard sandstone, 

 weathering light brown. It weathers also very cavei'nously, as 

 though calcareous, though a specimen examined at home did not 

 effervesce with acid. There are a few small lenticular nests of little 

 pebbles, but no pebbles were observed more than 1 inch in 

 diameter. The weathered plugs show marked bedding, which is 

 parallel to that of the series as a whole. There seem also a con- 

 centric structure and concentric colour banding. The jointing tends 

 to be radial. 



In both cases the Limestones penetrated by the pipes are 

 thoroughly marine, as shown by the fossils, though at Dwlban Point 

 the upper parts become somewhat sandy. No unconformity can be 

 observed between the beds, but just below the base of the sandstone 

 at the coast the Limestone becomes full of cracks, which widen 

 upwards into small fissures filled in with sand and pebbles. 



Whatever their origin, the pipes appear to be contemporaneous 

 with the series as a whole. There is no sign of collapse in the beds 

 above them, for the gentle downward bend in the great pipe affects 

 only the material within the pipe itself, and not the overlying beds ; 

 indeed, the tendency is to a heaping into domes above them. They 

 are suggestive of potholes, but there is no really coarse material 

 in them, pebbles, though present, being both rare and small. The 

 smaller plugs seem to be the more pebbly. 



The suggestion has been made that the beds overljnng the piped 

 Limestone represent fresh - water epi;sodes and upheaval, with 

 accompanying denudation.' Shales and sandstones in simiUir 

 positions in the Penmon area do, indeed, contain abundant plant- 

 remains, tliongh no pipes were observed by me there. But at 

 Dwlban Point the shale above the sandstone (7, Fig. 2) has yielded 

 a shell which, though very poorly preserved, Mr. E. T. Newton, 

 F.R.S., wlio was so good as to look at it for me, believes to be 

 Spirifera ovaJis, while the sandstone itself contains what seem to 

 be annelid castings. Mr. J. Bennie, formerly of the Geological 

 Survey of Scotland, has also very kindly examined the shale for 

 minute organisms, but has hitherto failed to find any. The whole 

 series therefore appears to be marine. The Assuring of the upper 

 surface of the Limestone, however, points to an interval of exposure 

 after hardening ; and it is interesting also to note that the Penmon 

 Sandstones above alluded to contain pebbles of Carboniferous Lime- 

 stone (Q.J.G.S., 1896, pp. 628, 629). We may conclude, then, that 

 the piping took place during an interval of shallowing, and, perhaps, 

 exposure of the sea-bottom. This was probably quite local, for the 

 sandstones in this region are for the most part of very limited extent. 



' By Mv. P. F. Kendall, F.G.S., during the discussion at the meetiuir of the British 

 Association. 



