There was a dull, muffled report, a sort of rumbling that seemed to extend away down under the earth and then echo back again until the ground near the mouth of the tunnel, where the party was standing, appeared to rock and heave. There followed a cloud of yellow, heavy smoke which made one choke and gasp, and Tom, seeing it, cried:  
"Down! Down, everybody! There's a back draft, and if you breathe any of that powder vapor you'll have a fearful headache! Get down, until the smoke rises!"
 
The tunnel contractors and their men understood the danger, for they had handled explosives before. It is a well-known fact that the fumes of dynamite and other giant powders will often produce severe headaches, and even illness. Tom's explosive contained a certain percentage of dynamite, and he knew its ill effects. Stretched prone, or crouching on the ground, there was little danger, as the fumes, being lighter than air, rose. The yellow haze soon drifted away, and it was safe to rise.
 
"Well, I wonder how much rock your explosive tore loose for us, Tom," observed Job Titus, as he looked at the thin, yellowish cloud of smoke that was still lazily drifting from the tunnel.
 
"Can't tell until we go in and take a look," replied the young inventor. "It won't be safe to go in for a while yet, though. That smoke will hang in there a long time. I didn't think there'd be a back draft."
 
"There is, for we've often had the same trouble with our shots," Walter Titus said. "I can't account for it unless there is some opening in the shaft, connecting with the outer air, which admits a wind that drives the smoke out of the mouth, instead of forward into the blast hole. It's a queer thing and we haven't been able to get at the bottom of it."
 
"That's right," agreed his brother. "We've looked for some opening, or natural shaft, but haven't been able to find it. Sometimes we shoot off a charge and everything goes well, the smoke disappears in a few minutes. Again it will all blow out this way and we lose half a day waiting for the air to clear. There's a hidden shaft, or natural chimney, I'm sure, but we can't find it."
 
"Thot blast didn't make much racket," commented Tim Sullivan. "I doubt thot much rock come down. An' thot's not sayin' anythin' ag'in yer powder, lad," he went on to Tom.
 
"Oh, that's all right," Tom Swift replied, with a laugh. "My explosive doesn't work by sound. It has lots of power, but it doesn't produce much concussion."
 
"We've often made more noise with our blasts," confirmed Job Titus, "but I can't say much for our results."
 
They were all anxious, Tom included, to hurry into the tunnel to see how much rock had been loosened by the blast, but it was not safe to venture in until the fumes had been allowed to disperse. In about an hour, however, Tim Sullivan, venturing part way in, sniffed the air and called:
 
"It's all right, byes! Air's clear. Now come on!"
 
They all hurried eagerly into the shaft, Mr. Damon stumbling along at Tom's side, as anxious as the lad himself. Before they reached the face of the cliff against which the bore had been driven, and which was as a solid wall of rock to further progress, they began to tread on fragments of stone.
 
"Well, it blew some as far back as here," said Walter Titus. "That's a good sign."
 
"I hope so," Tom remarked.
 
There were still some fumes noticeable in the tunnel, and Mr. Damon complained of a slight feeling of illness, while Koku, who kept at Tom's side, murmured that it made his eyes smart. But the sensations soon passed.
 
They came to a stop as the face of the cliff loomed into view in the glare of a searchlight which Job Titus switched on. Then a murmur of wonder came from every one, save from Tom Swift. He, modestly, kept silent.
 
"Bless my breakfast orange!" cried Mr. Damon. "What a big hole!"
 
There was a great gash blown in the hard rock which had acted as a bar to the further progress of the tunnel. A great heap of rock, broken into small fragments, was on the floor of the shaft, and there was a big hole filled with debris which would have to be removed before the extent of the blast could be seen.
 
"That's doing the work!" cried Job Titus.
 
"It beats any two blasts we ever set off," declared his brother.
 
"Much fine!" muttered the Peruvian foreman, Serato.
 
"It's a lalapaloosa, lad! Thot's what it is!" enthusiastically exclaimed Tim Sullivan. "Now the black beggars will have some rock to shovel! Come on there, Serato, git yer lazy imps t' work cartin' this stuff away. We've got a man on th' job now in this new powder of Tom Swift's. Git busy!"
 
"Um!" grunted the Indian, and he called to his men who were soon busy with picks and shovels, loading the loosened rock and earth into the mule-hauled dump cars which took it to the mouth of the tunnel, whence it was shunted off on another small railroad to fill in a big gulch to save bridging it.
 
Tom's first blast was very successful, and enough rock was loosed to keep the laborers busy for a week. The contractors were more than satisfied.
 
"At this rate we'll finish ahead of time, and earn a premium," said Job to his brother.
 
"That's right. You didn't make any mistake in appealing to Tom Swift. But I wonder if Blakeson & Grinder have given up trying to get the job away from us?"
 
"I don't know. I'd never trust them. We must watch out for Waddington. That bomb on the vessel had a funny look, even if it was not meant to kill Tom or me. I won't relax any."
 
"No, I guess it wouldn't be safe."
 
But a week went by without any manifestation having been made by the rival tunnel contractors. During that week more of Tom's explosive arrived, and he busied himself getting ready another blast which could be set off as soon as the debris from the first should have been cleared away.
 
Meanwhile, Professor Bumper, with his Indian guides and helpers, had made several trips into the mountain regions about Rimac, but each time that he returned to the tunnel camp to renew his supplies, he had only a story of failure to recite.
 
"But I am positive that somewhere in this vicinity is the lost Peruvian city of Pelone," he said. "Every indication points to this as the region, and the more I study the plates of gold, and read their message, the more I am convinced that this is the place spoken of.
 
"But we have been over many mountains, and in more valleys, without finding a trace of the ancient civilization I feel sure once flourished here. There are no relics of a lost race—not so much as an arrow or spear head. But, somehow or other, I feel that I shall find the lost city. And when I do I shall be famous!"
 
"Mr. Damon and I will help you all we can," Tom said. "As soon as I get ready the next blast I'll have a little time to myself, and we will go with you on a trip or two."
 
"I shall be very glad to have you," the bald-head............