"what is the matter?" asked mr. damon, catching the glance between tom and the contractor. "is there anything wrong with south america—peru? i know they have lots of revolutions in those countries, but i don't believe peru is what they call a 'banana republic'; is it?"

"no," and mr. titus shook his head. "it isn't a question of revolutions."

"but it's something!" insisted mr. damon. "bless my ink bottle! but it's something. as soon as i mention peru, tom, you and mr. titus eye each other as if i'd said something dreadful. out with it! what is it?"

"it's just—just a coincidence," tom said. "but go on, mr. damon. finish what you have to say and then we'll explain."

"well, i guess i've told you all you need to know for the present. i went into this wholesale drug concern, hoping to make some money, but now, on account of the trouble down in peru, we stand to lose considerable unless i can get back the cinchona concession."

"what does that mean?" tom asked.

"well, it means that our concern secured from the peruvian government the right to take this quinine-producing bark from the trees in a certain tropical section. but there has been a change in the government in the district where our men were working, and now the privilege, or concession, has been withdrawn. i'm going down to see if i can't get it back. and i want you to go with me."

"and i came here for very nearly the same thing," went on mr. titus. "that is where the coincidence comes in. it is strange that we should both appeal to mr. swift at the same time."

"well, tom's a valuable helper!" exclaimed mr. damon. "i know him of old, for i've been on many a trip with him."

"this is the first time i have had the pleasure of meeting him," resumed the tunnel contractor, "but i have heard of him. i did not ask him to go to south america for us. i only wanted to get some superior explosive for my brother, who is in charge of driving the railroad tunnel through a spur of the andes. i look after matters up north here, but i may have to go to peru myself.

"as i told mr. swift, i had read of his invention of the giant cannon and the special powder he used in it to send a projectile such a distance. the cannon is now mounted as one of the pieces of ordnance for the defense of the panama canal, is it not?" he asked tom.

the young inventor nodded in assent.

"having heard of you, and the wonderful explosive used in your big cannon," the contractor went on, "i wrote to my brother that i would try and get some for him.

"you see," he resumed, "this is the situation. back in the andes mountains, a couple of hundred miles east of lima, the government is building a short railroad line to connect two others. if this is done it will mean that the products of peru—quinine bark, coffee, cocoa, sugar, rubber, incense and gold can more easily be transported. but to connect the two railroad lines a big tunnel must be constructed.

"my brother and i make a specialty of such work, and when we saw bids advertised for, our firm put in an estimate. there was some trouble with a rival firm, which also bid, but we secured the contract, and bound ourselves to have the tunnel finished within a certain time, or forfeit a large sum.

"that was over a year ago. since then our men, aided by the native indians of peru, have been tunneling the mountain, until, about a month back, we struck a snag."

"what sort of snag?" tom asked.

"a snag in the shape of extra hard rock," replied the tunnel contractor. "briefly, paleozoic rocks make up the eastern part of the andean mountains in peru, while the western range is formed of mesozoic beds, volcanic ashes and lava of comparatively recent date. near the coast the lower hills are composed of crystalline rocks, syenite and granite, with, here and there, a strata of sandstone or limestone. these are, undoubtedly, relics of the lower cretaceous age, and we, or rather, my brother, states that he has found them covered with marine tertiary deposits.

"now this mesozoic band varies greatly. porphyritic tuffs and massive limestone compose the western chain of the andes above lima, while in the oroya valley we find carbonaceous sandstones. some of the tuffs may be of the jurassic age, though the cretaceous period is also largely represented.

"now while these different masses of rock formation offer hard enough problems to the tunnel digger, still we are more or less prepared to meet them, and we figured on a certain percentage of them. up to the present time we have met with just about what we expected, but what we did not expect was something we came upon when the tunnel had been driven three miles into the mountain."

"what did you find?" asked tom, who knew enough about geology to understand the terms used. mr. damon did not, however, and when mr. titus rolled off some of the technical words, the drug investor softly murmured such expressions as

"bless my thermometer! bless my porous plaster!"

"we found," resumed mr. titus, "after we had bored for a considerable distance into the mountain, a mass of volcanic rock which is so hard that our best diamond drills are dulled in a short time, and the explosives we use merely shatter the face of the cutting, and give us hardly any progress at all.

"it was after several trials, and when my brother found that he was making scarcely any progress, compared to the energy of his men and the blasting, that he wrote to me, explaining matters. i at once thought of you, tom swift, and your powerful explosive, for i had read about it.

"now then, will you sell us some of your powder—explosive or whatever you call it—mr. swift, or tell us where we can get it? we need it soon, for we are losing valuable time."

mr. titus paused to draw on a piece of paper a rough map of peru, and the district where the tunnel was being constructed. he showed where the two railroad lines were, and where the new route would bring them together, the tunnel eliminating a big grade up which it would have been impossible to haul trains of any weight.

"what do you say, mr. swift?" the contractor concluded. "will you let us have some of your powder? or, better still, will you come to peru yourself? that would suit us immensely, for you could be right on the ground. and you could carry out your plan of going with your friend here," and mr. titus nodded toward mr. damon. "that is, if you were thinking of going."

"well, i was thinking of it," tom admitted. "mr. damon and i have been on so many trips together that it seems sort of natural for us to 'team it.' i have never been to peru, and i should like to see the country. there is only one matter though, that bothers me."

"what is it?" asked mr. titus quickly. "if it is a question of money dismiss it from your mind. the peruvian government is paying a large sum for this tunnel, and we stand to make considerable, even if we were the lowest bidders. we can afford to pay you well—that is, we shall be able to if we can complete the bore on time. that is what is bothering me now—the unexpected strata of hard rock we have met with, which seems impossible to blast. but i feel sure we can do it with the explosive used in your giant cannon."

"that is just the point!" tom exclaimed. "i am not so sure my explosive would do."

"why not?" the tunnel contractor asked. "it's powerful enough; isn't it?"

"yes, it is powerful enough, but whether it will have the right effect on volcanic rock is hard to say. i should like to see a rock sample."

"i can telegraph to have some sent here to you," said mr. titus eagerly. "meantime, here is a description of it. i can read you that"; and, taking a letter from his pocket, he read to tom a geological description of the hard rock.

"hum! yes," mused tom, as he listened. "it seems to be of the nature of obsidian."

"bless my watch chain!" cried mr. damon. "what's that?"

"obsidian is a volcanic rock—a sort of combination of glass and flint for hardness," tom explained. "it is brittle, black in color, and the natives of the admiralty islands use it for tipping their spears with which they slay victims for their cannibalistic feasts."

"bless my—bless my ear-drums!" gasped mr. damon. "cannibals!"

"obsidian was also used by the ancient mexicans to make knives and daggers," tom went on. "when cortez conquered mexico he found the priests cutting the hearts from their living victims with knives made from this volcanic glass-like rock, known as obsidian. it may be that your brother has met with a vein of that in the tunnel," tom said to the contractor.

"possibly," admitted mr. titus.

"in that case," tom stated, "i may have to use a new kind of explosive. that used for my giant cannon would merely crumble the hard rock for a short distance."

"then will you accept the contract, and help us out?" asked mr. titus eagerly. "we will pay you well. will you come to peru and look over the ground?"

"and kill two birds with one stone, and come with me also?" put in mr. damon.

tom pondered for a moment. he was about to answer when the tunnel contractor, who was looking from the library window, suddenly jumped from his chair crying:

"there he is again! once more dogging me!"

as he rushed from the room, tom and mr. damon had a glimpse of a face at one of the low library windows—a face that had an evil look. it disappeared as mr. titus ran from the room.