All the high hills, and the mountains were covered Therefore, there were hills and mountains before the flood. Deists, and other infidels, would persuade us that this was impossible, because of the vast height of divers hills and mountains. But, not to mention here that this fact has been established by the universal consent of all nations, that there was a general deluge which over-flowed the whole world, and that it has been demonstrated by different writers that there is in nature a sufficient quantity of water to deluge it, concerning both which see the Encyclopædia Britannica; it will be sufficient to observe here, that this cannot be thought impossible by any one who believes in the existence of such a being as Jehovah, a God of infinite power, to whom it surely was as easy to bring forth a sufficiency of water for this purpose, as it was to create all things by the word of his power, or to say, Let there be light, and there was light. It is evident Moses, the historian, makes no difficulty on this subject. So far from questioning whether the quantity of water in the earth and atmosphere was sufficient, he thought the sources from whence it came were not exhausted, since both of them required to be stopped by the same almighty hand that opened them, lest the flood should increase more than it actually did.
Related Commentaries of Genesis 7:19
Genesis 7:19-20
19 And the waters prevailed exceedingly upon the earth; and all the high hills, that were under the whole heaven, were covered.
20 Fifteen cubits upward did the waters prevail; and the mountains were covered.