13.

To what we cited before concerning the temple of Ammon and Egypt, Eratosthenes adds, that to judge from appearances, Mount Casius353 was formerly covered by sea, and the whole district now known as Gerra lay under shoal water touching the bay of the Erythræan Sea,354 but was left dry on the union355 of the [Mediterranean] Sea [with the ocean]. A certain amphibology lurks here under this description of the district lying under shoal water and touching the bay of the Erythræan Sea; for to touch356 both means to be close to, and also to be in actual contact with, so that when applied to water it would signify that one flows into the other. I understand him to mean, that so long as the strait by the Pillars of Hercules remained closed, these marshes covered with shoal-water extended as far as the Arabian Gulf, but on that passage being forced open, the Mediterranean, discharging itself by the strait, became lower, and the land was left dry.

On the other hand, Hipparchus understands by the term touching, that the Mediterranean, being over-full, flowed into the Erythræan Sea, and he inquires how it could happen, that as the Mediterranean flowed out by this new vent at the Pillars of Hercules, the Erythræan Sea, which was all one with it, did not flow away too, and thus become lower, but has always retained the same level? and since Eratosthenes supposes the whole exterior sea to be confluent, it follows that the Western Ocean357 and the Erythræan Sea are all one; and thus [remarks Hipparchus] as a necessary consequence, the sea beyond the Pillars of Hercules, the Erythræan Sea, and that also which is confluent with it,358 have all the same level.