The rock structure of the cave arches is displayed in very beautiful ways in this cavern, but the most interesting feature is the remnant of an old cave floor. The cavern was evidently formed in pre-Glacial times, and the vast quantities of clay that plug it up almost entirely now must have been carried in by the ice. After the glaciers had receded, the normal agencies began their work again; a stalagmite floor was formed by the drip of water from the roof, depositing a layer of calcite; this in the course of time was broken down again, and now leaves a kind of high-water mark all round the walls of the cavity. [Illustration: THE OGO, NEAR ABERGELE. _Photo by E. A. Baker._] [Illustration: INSIDE THE OGO, NEAR ABERGELE. _Photo by E. A. Baker._] The line of the fissure creating the upward chasms inside the cave can be traced in the external configuration of the cliff; in sundry vertical openings in the face, and in the clean-cut walls, where sheer masses have fallen away, broken at the joints. Similar joints and fissures played a part in the formation of a lower tier of caves, which we explored next. The first was only a yard or two wide, but very lofty, and its floor was composed of a level bed of sand and clay. This gradually rose as we walked into the darkness, until the cave ended more abruptly even than the last. We noticed pebbles of Bunter sandstone in the floor, and the next cave produced many more examples of the same stone, which must have been brought from a long distance, the nearest strata corresponding to it being in Wirral. At the back of this next cave a bank of cave earth and boulder clay was piled right up to the roof, so steeply that it was not too easy a climb to the summit. Arrived there, we found no possible egress; but a horizontal tunnel, a sort of squint or hagioscope probably more than forty feet long, gave us a peep through the rocky cliff out to the sunlight. We set out forthwith to discover the outside orifice of this curious hole, and found it came out on a ledge in the face of the cliff, hard by an open platform which had a very queer look about it. On examination this proved to be the floor of an old cave that had been destroyed by the quarrymen. Half-embedded in thick clay were a number of stalagmite pedestals, and a floor of stalagmite underneath several feet in depth, surmounting a thick bed of boulder clay stuck full of Bunter pebbles. It was obvious that the quarrymen, coming across this mass of useless material, had not troubled to attack the solid layer of stalagmite above it. The remains of stalactites and stalagmite curtains still adhered to the neighbouring cliff.