13. The study of the geological beds attests, as has previously been stated, to successive formations, which have gradually changed the form of the globe, and divided its history into many epochs. These epochs constitute that which is called geologic periods, the knowledge of which is necessary to establish a true Genesis. Geologists count six principal periods, which they have designated as follows: first the primary, second the transition, third the secondary, fourth the tertiary, fifth the deluge, sixth the post-deluge or present period. Rocks formed during the duration of each period are called thus: primitive, transition, secondary rocks, etc. One says that such and such rocks, such and such fossils, are found in rocks of such and such periods.