All this while the boat was in plain view, sailing on a course parallel to theirs, at a distance of half a mile. It had now outstripped them, and Uncle Will said it ought to turn in soon toward the shore. It became evident before long, however, that the craft was in trouble. She was well out from the land, but seemed to be stationary. The shore party, slowly as they moved, now steadily gained on her, and at length they could see the two occupants standing on the bow and thrusting oars or poles into the water in different places. "She's aground!" exclaimed Uncle Will, after a moment's observation; "and the tide's going out. This is a pretty fix!" "Can we do anything?" asked David, eager to go to the rescue. "Oh! we might as well go on to the cave. It's not far now. We'll leave the sleds there, and then see what can be done. I don't think we can wade out to the boat yet, for there are two or three channels this side of her." So on they plodded once more. The cave was a great hole in the base of a cliff, and would comfortably contain a score of men, being ten feet high, fifteen feet deep, and eight feet wide. The boys wondered if it had ever been the haunt of robbers or pirates,--a fancy which the still smouldering embers of a camp-fire left by the Mysterious Thirty-six seemed to bear out. Indeed, Roly examined the interior carefully, half expecting to see the glimmer of gold coins in the darker crevices, but he found only a piece of canvas which might have been part of a money-bag. A closer examination showed that it was plentifully sprinkled with flour, and probably had never been used for anything more romantic. In all directions the snow had been trampled hard, and numerous bits of rope, and a tin can or two which no keen-eyed Indian had yet appropriated, showed how recently the place had been deserted. Along the beach was a row of crotched poles, most of them still upright, where the numerous tents had stood. David pointed these out to Roly delightedly, observing that poles and spruce boughs in abundance were ready cut for them. The receding tide had now uncovered miles of mud flats, and Uncle Will declared himself ready to try to reach the boat. Long Peter was left at the cave to cut firewood, but the boys preferred to accompany their uncle, and started off in high spirits. They advanced with some difficulty, for the mud was often adhesive, clogging their boots at every step until they came to sandier stretches. At all the channels, most of which were easily crossed, although the water was running swiftly seaward, Uncle Will took the lead, prodding the ground carefully with a pole as he walked, to guard against quicksands. In this manner they reached a deep channel a few rods from the stranded sloop.