"The engines won't back her out?" he asked in a voice harsh and rough from anxiety. "No. I'm sorry, Barr, but we're in a mighty bad fix. This submarine cliff must be of a sort of blue clay formation that is common off this coast. We have apparently driven into it so far that nothing short of an earthquake would dislodge us." "An earthquake?" "Yes; such a spasm of nature alone can set us free." "Then we are doomed to remain here." "Not of necessity; we have still a chance of escape." "What do you mean?" "That my plan offers a mere chance." "Then let us not delay in putting it into execution." "But it is a dangerous one!" "Never mind that. Nothing could be more serious than our present predicament." "Very well then, we will try out my idea. It's our last chance." "Our last chance!" The words sounded to the boys almost like a requiem. Plainly enough, whatever Ensign Hargreaves' plan might be, there were dangers attached to it, and no light dangers, either, to judge from his grave tones. Eagerly they awaited his next words. "My plan is nothing more nor less than this," he said; "I propose to create an earthquake." "To _create_ an earthquake!" Mr. Barr echoed the words, staring at the ensign as if he thought he had gone suddenly insane. "Precisely. I intend to produce by artificial means an eruption which will destroy enough of this cliff to set us free, or else blow the _Peacemaker_ herself into atoms." Mr. Barr buried his head in his hands. Skillful inventor and scientific expert though he was, the last words of the naval officer had sapped even his iron courage. "Is there no other way?" "No other way. It's a gamble for our lives." "What do you propose doing?" asked Mr. Barr in a strange, broken voice. "As I said, to create an artificial earthquake." "I am unable to follow you." "Then I'll make it clearer. In the torpedo compartment forward you have six Red Head torpedoes fully charged with gun cotton?" "Yes." The inventor was regarding the naval officer with intense interest now, and the boys also stood transfixed, their eyes riveted on the ensign as he unfolded his plan. "What I propose to do," he continued, "is to discharge from the side torpedo tubes two torpedoes. They will be aimed at the cliff and, of course, when they strike it, will explode." "But in that case our bow would be blown off also, and we should perish almost instantly," declared Mr. Barr. "Wait a minute. I didn't say we would discharge them _directly_ at the cliff. What I propose doing is this: We will aim one on each side of the spot where our bow drove in, taking care to train the tubes so that the torpedoes will not strike too near." "Yes, the tubes are movable. That is one of the features of the _Peacemaker_." "Very well, then, they will be as easy to train in any desired direction as a rapid fire gun." "Exactly. But I never thought when I designed them that I might some day owe my life to that very feature."