Read it through once

But the feature of the place is a short column that rises from the middle of the marble pavement of the chapel, and marks the exact centre of the earth. The most reliable traditions tell us that this was known to be the earth's centre, ages ago, and that when Christ was upon earth he set all doubts upon the subject at rest forever, by stating with his own lips that the tradition was correct. Remember, He said that that particular column stood upon the centre of the world. If the centre of the world changes, the column changes its position accordingly. This column has moved three different times of its own accord. This is because, in great convulsions of nature, at three different times, masses of the earth --whole ranges of mountains, probably--have flown off into space, thus lessening the diameter of the earth, and changing the exact locality of its centre by a point or two. This is a very curious and interesting circumstance, and is a withering rebuke to those philosophers who would make us believe that it is not possible for any portion of the earth to fly off into space.