150 Journal of Travel and Natural History 



but at a fomier and no very distant period, a depression un- 

 doubtedly must have taken place. 



But these facts not only prove the depression of the Red Sea, 

 but give a date for its occurrence. It must have taken place sub- 

 sequent to the appearance on the earth of the present jackal, 

 hyena, wild ass, antelope ; in fact, during the recent epoch. But 

 more than that, it tells us that it must have taken place subse- 

 quently to the elevation of the Sahara, for the same desert inhabitants 

 are found in both. We know from the shells found in the deposits 

 and sands of that desert that it was a sea during the Miocene and 

 Quaternary epochs. A similar desert exists'in the southern half of 

 Arabia, and but for the intervention of the Red Sea and the high- 

 lands of Abyssinia, there would be one continuous stretch of sandy 

 desert, the bed of an antient sea, from the Atlantic to the Persian 

 Gulf. But the Red Sea must be subsequent in date to the appear- 

 ance of these desert animals, and, so far as regards Abyssinia, 

 geology teaches us that Avhenever a great elevation of one portion 

 of the earth's surface has taken place, it has been accompanied by 

 a corresponding depression of another portion parallel to and 

 alongside of the part elevated ; and the compensatory relation of 

 the two phenomena shews that their occurrence must be nearly 

 simultaneous, or rather that the depression must have slightly pre- 

 ceded the elevation. For, assuming that the earth is a liquid molten 

 mass in process of cooling, surrounded by a crust already cooled 

 and solidified, it is not easy to understand how any first impulse of 

 ebullition causing a movement of elevation should be given ; but 

 it is very easy to understand, that as the process of cooling goes 

 on, and the consequent shrinkage follows, the hardened crust will 

 in some places be left without support, and in these it will settle 

 down like the roof of a coal mine when the props are withdrawn ; 

 as it does so on the molten matter it will sink in it, to a certain 

 extent displacing some, and causing it to surge up on either side, 

 producing earthquakes, breaking the cohesion of the superincum- 

 bent strata, and finding exit by fissures and volcanoes. Eruptions 

 are usually spoken of as the result of an access of intensity in the 

 igneous action — a fresh hand at the bellows ; but although at the 

 immediate scene of action they assume this phase, in point of fact 

 they are the very reverse — they are indications of gixviter cooling 

 instead of greater heat in the interior of the earth — they are the 

 mere splashing caused by the falling in of a portion of the cooled 

 roof. In the i)resent case the depression of the Red Sea and the 



