As there was no clue to the level reached by the tide, I tried back on the possibility of gauging it by measuring from low water, so far as my memory of the tides might serve. Judging by the depth of the water, so far as I had gone, the fall of the floor level must here have been some three feet. The floor level of the cave was almost that of low water, except where it dipped under the overhanging roof, or where was the ascending grade up to the pool in which the treasure boxes lay. As here on the border of the North Sea, with no estuary to increase tidage, the normal rise of the tide is between eleven and twelve feet, we had to account for another eight or nine feet for the rise of the tide. The ledge was about a foot above the surface of the water. If my calculations were correct there was head room and breathing space, for as I stood on the ledge the top of my head was still about two feet from the highest point of roof over us. I could not, however, be certain of my calculations, within a couple of feet. If, therefore, we could keep our place on the shelf of rock and endure the cold we might yet win through. The cold was a serious matter. At Cruden where the full sweep of the icy current from the North Sea runs in shore, the water is grievously cold, even in the hottest summer time. Already we were feeling the effects of our wet clothes, even in this silent cavern where the heat seemed to be much more than outside. When we had been looking at the jewels, I had myself felt the chill, and could feel Marjory shiver now and again. Indeed, I had been about to suggest our returning when I made the discovery of the rising tide. It was no use regretting, however. We were caged in the cavern; and our only chance was to hold on somehow, till the tide should fall again. The practical side of Marjory's mind was all awake. It was she who quietly refilled the two lamps, and, with much spluttering of the wick at first, lighted again the one which I had let fall into the water. When both lamps were ready, she put out the torch and placed it in the tin box which she handed to me, saying: "We may need all the air we can get for our breathing, and the torches would burn it up. We must have two lamps lest one should fail. Shove the box as far as it will go into the corner of the cave; it will be safe there--as safe as us at any rate, for it will be over our heads."