Note 15 — Chapter XVII

Father Ravennes was considerably out in his estimate. The continent of Gondwana of which he spoke dates from the first part of the secondary era in which the great Hercynian upheaval took place. The discovery of radium has given us a method of establishing the distance of that era from our time as about four million years. If we admit then that the Gondwana ravine discovered by Lursac and Ravennes only dated from the end of the secondary era it would be separated from the present day by the entire tertiary era and the beginning of the quaternary era in which we now are. According to the calculations of Dana, of Lord Kelvin and of Edmond Perrier, the tertiary era and what has elapsed of the quaternary make a total of at least one million five hundred thousand years.