Four days into the Earth and we hit disaster. A dead end! Did we choose the wrong path? Or was this a cave-in that occurred in the centuries after Saknussemm?

Should we turn round and admit we have wasted more than a week's supplies for nothing? Or what if it turns out this was the right way? Should we use our gun cotton and blast the blockage away? But what if that causes the tunnel to collapse? Or should we do something else?