The two river travelers find that many sand funnels have been formed around the island and expect that the unexplained creatures that they had previously witnessed are the cause of these indentations.
"It's those sand-funnels," exclaimed the Swede, when the tent was up again and the firelight lit up the ground for several yards about us. "And look at the size of them!"
All round the tent and about the fireplace where we had seen the moving shadows there were deep funnel-shaped hollows in the sand, exactly similar to the ones we had already found over the island, only far bigger and deeper, beautifully formed, and wide enough in some instances to admit the whole of my foot and leg.
Neither of us said a word. We both knew that sleep was the safest thing we could do, and to bed we went accordingly without further delay, having first thrown sand on the fire and taken the provision sack and the paddle inside the tent with us. The canoe, too, we propped in such a way at the end of the tent that our feet touched it, and the least motion would disturb and wake us.”
The Willows, by Algernon Blackwood