Heuglhis " Rcise Nach Abessinieti " 151 



elevation of the highlands of Abyssinia must be counterparts in 

 the same transactions. By his Ust of Saharan and Arabian mam- 

 mals which occur in the islands of the Red Sea, Von Heughn 

 furnishes proof that they have been cut off from the mainland by 

 the sinking of the bed of that sea ; and, curiously enough, if infor- 

 mation which he received regarding the animals which occur in 

 the Tana Sea turns out to be true, he, in like manner, furnishes us 

 with means of proving the elevation of that inland lake from the 

 bottom of the sea, and that too at a date subsequent to animal life 

 having put on its present form. The Tana Sea is a large sheet of 

 water 5732 feet above the level of the sea— according to Ruppell — 

 lying in a hollow, surrounded by lofty mountains. It is very deep. 

 Heuglin found no bottom with a line of 197 yards. Its bed is 

 said to be cone-shaped, and Ruppell has supposed it to be an 

 immense extinct crater. This supposition we think wholly unten- 

 able : craters are not things that increase indefinitely in dimensions 

 according to the force and magnitude of the forces engaged. 

 They are phenomena which have a natural limit, as the bubble of 

 foam at the base of the falls of Niagara is no larger than that from 

 a mill wheel, and the size of the crater must bear a deteniiinate pro- 

 portion to the height and spread of the cone. Now, the Tana Sea 

 covers sixty square German miles, and a crater of that extent must 

 have had a cone at least four times as many miles in height, or 

 else have speedily been cooled over and reduced to several distinct 

 cones of normal size scattered over the space. Rejecting, then, 

 all idea of the Tana Sea being an extinct crater, it may be a collec- 

 tion of water accumulated from the rainfall of the surrounding 

 mountains, or the remains of a part of a sea-bottom, raised up — 

 mountains, bed, basin, sea, and all — during the course of the eleva- 

 tion of the district generally. There were, no doubt, both general 

 elevation and special increase of height by the jDouring out of vol- 

 canic matter. The fact which suggests this view is the following 

 remark by Heuglin : — 



"Besides the hippopotamus, which dwells in great numbers in the 

 Tana Sea, there is, as I am well informed, here found another 

 animal, probably a manatus, called the Ja-Baher-Dedsa., or Aila 

 Auli ; the first name means a sea calf." — (p. 289.) "Probably this 

 animal is identical with the Arha-Bih, a large beast called the Sibda 

 that is met with in the tributaries of the Mareb." — (p. 247). The 

 Tana Sea is not the only inland habitat assigned to the manatee 

 in Africa. It is said by Barth and others to occur in Lake Tsad ; 



