Frank left the cavern in a moment and walked along the beach toward the
campfire. His thought was to gather embers and fresh fuel and build up a
blaze at the end of the cave which would reveal every inch of the
interior. He was certain that Jack had not left the place, and decided
that he had fallen into some hidden opening which had escaped his own
investigation.
As he bent over the remains of the fire he heard a rattle of small
stones, and, looking up, saw Pat coming down the declivity from the
plateau where the tents had been set up. The incline was steep, and at
times Pat was rolling rather than walking. He was in his shirt sleeves
and bareheaded. At last his red head pitched toward the lake like a
meteor in downward flight.
Frank rushed forward and caught him as he struck the beach, thus saving
him from an impromptu bath. Pat struggled to his feet in an instant,
rubbed his legs and arms to see if any bones had been broken, and then
turned his head and looked up the incline.
"Talk about shooting the chutes!" he exclaimed. "I wonder what time I
made coming down?"
"Sure you're not hurt?" asked Frank anxiously.
"Every inch of my body has three bruises, one on top of the other," Pat
replied, "but I guess I'm able to walk. Say, but that was a
roller-coaster glide!"
"Why did you try such a foolish caper?" asked Frank.
"Why, I saw you boys here," was the reply, "and started down. You know
the rest, as the yellow-covered books say. What you boys doing here,
wasting your time, with the bacon burning to a crisp?"
"We came here to investigate," was the reply, "and Jack went into the
cavern, and vanished--just vapored into thin air. I'm going to build a
fire in there and see if I can't condense him!"
"Well," Pat said, listening, "he may have vanished physically, but his
voice appears to be on deck yet."
Three sharp calls came from the cavern, and both boys dashed inside.
There was no doubt now that Jack's voice, at least, had condensed, for
the shouts coming from the back of the cavern were both hearty and
imperative.
"Hi, there!" Jack called. "Pry this stone out of the doorway!"
"Where are you?" demanded Pat. "Which one of the walls do you want us to
push in? You're a nice chump, getting in a scrape like this!" he added,
with a laugh which must have been exasperating to the unseen boy.
"You'll find a crevice where the back of the cave joins the south wall,"
Jack said, his voice coming faintly to the ears of his chums. "Put your
fingers in and pull. The blooming door opens outward. Hurry! It's
stifling in here!"
After burning nearly all the matches they had in their pockets, and
scorching their fingers on the short sticks, Pat and Frank discovered
the crevice spoken of and inserted the ends of their fingers.
"Pull!" yelled Jack. "Pull, you loafers! It is moving!"
In a moment the south half of the back wall swung out so suddenly that
both boys were thrown from their feet and Jack, who had been pushing
with his whole strength, came tumbling on top of them as they lay on the
floor of the cavern.
"What sort of a combination is this, anyway?" demanded Pat, struggling
to his feet. "If I get any more bumps to-day I'll be taking something
that belongs to some one else. I've had my share."
Frank sprang to the opening as soon as he could disentangle himself from
the collection of arms and legs and looked in. All was dark and still
inside, and a gust of dead air struck him in the face. Pat, leaning over
his shoulder, laid a hand on the rock which had opened so strangely, and
the next instant it closed softly, sliding into the opening like a door
operated by well-oiled machinery.
"Now you've done it!" Frank exclaimed, disgustedly, as Pat threw himself
against the stone in a vain effort to force it open again.
"No harm done," Jack exclaimed. "There's only a stinking cavern in
there. Wow! I can feel snakes and lizzards crawling on me now! Come! Let
us get into the open air. Stifles like a grave in here."
The boys hastened outside and stood meditatively before the shining
waters of the lake, each one trying to think clearly concerning what had
taken place. They believed themselves--or had believed, rather--miles
away from any trace of civilization, and yet here was a practical door
of rock at the end of a cave almost under the great divide.
"We've found something," Frank said, at length. "That thing in there
never happened. Human hands fashioned that door for some secret purpose.
And it wasn't Indians, either."
"I guess we've run up against a band of train robbers," suggested Jack,
with a grin.
"Probably the entrance to some deserted mine," Pat put in. "This region
has been searched for gold for fifty years. I've heard of mines being
concealed by moving stones."
"Well," Frank said, after a short silence, during which all listened for
some indication of the immediate presence of the men who had been seen
to row around the green point a short time before, "whatever the game
is, we've got to remove every trace of our visit. When they come back
they probably won't notice the tracks we have made, for there were
plenty about before we came here, but we must gather up all the
match-ends we left in there and leave the door as we found it."
"I found it open and walked in," Jack said, "and then it closed. Whew! I
felt like I was being shut up in a tomb!"
"How large a place is it in there?" asked Pat.
"Don't know," was the reply. "I had no matches with me, and so could not
see a thing."
"Then we won't have to open the door again to clean up any muss," Frank
said, moving toward the entrance to the cavern.
"I wouldn't go in again for a thousand dollars," Jack cried. "If you
leave it to me, the place is haunted. I heard groans in there."
Frank paused at the entrance and turned back. His matches were about
gone, and so he took a burning stick from the fire, added two dry
faggots to it, waited until the three burst into flame, and then entered
the cave.
To gather up the half-burned matches which had been scattered over the
floor was the work of only a moment.
"Now you'll have to open the door, if you leave it as I found it," Jack
said, looking in from the mouth. "Pat will help you."
"Come on in, both of you," Frank directed.
"Not me!" cried Jack. "I hear bones rattling!"
The boys thought he was joking at first, but it soon appeared that he
was in sober earnest, so Pat and Frank, by exerting their entire
strength, managed to open the door without his assistance.
"You're afraid of the dark!" Pat taunted, as the boys gathered around
the fire again.
"I'm not half as afraid of the dark as you are of an aeroplane," Jack
replied. "If I ever see you going up in a 'plane, I'll go in there
alone."
"Don't you ever forget that," Pat grinned.
"Oh, I'll be game, all right," was the reply.
Before leaving the beach for the camp the boys walked to the point
around which the boat had gone and scanned the lake and its shores
through the field-glass. There was no sign of life anywhere, except
where the birds swung from forest limbs back from the rim of the lake
and called each other through the sultry air.
Reaching the camp after a weary climb, they did full justice to the meal
which Pat had prepared, though the bacon and the hoecakes were stone
cold, or at least as cold as anything could be in that glare of
sunlight. Then, the dishes washed and the beds prepared for the night,
they sat down to watch the lake and the sky to the south, for it was now
the general belief that Ned would make his appearance with the aeroplane
which had been promised by the government officials.
The point they had last visited, as well as the location of the fire,
was in full view of the plateau, so the boys made no efforts to conceal
their presence there. The men who had been observed in the boat must
have noted their presence on the plateau before taking their leave.
Perhaps, they reasoned, they had taken their departure because of this
invasion.
The sun sank lower and lower in the sky, turning the plateau and the
smooth waters of the lake to gold, still there were no signs of Ned, no
indications of the return of the boat to the place from which it had
been launched. Half an hour after dark, Frank, who was looking through
the field-glass, caught sight of light in the south which did not appear
to come from any star.
"Here he comes!" he cried. "That's an aeroplane, all right!"
As the light drew nearer, traveling rapidly, the sharp explosions of the
gasoline engine became audible. Then a light flickered over the upper
plane, passed off, and swept the white surface again.
"How does he make that?" demanded Pat. "Looks like a great question
mark."
"That's what it is," Frank exclaimed. "Now, what does he mean by it?"