320 Revieics — T. M. Reacle, on the Two Americas. 



In Parkinson's "Organic Eemains"^ there is described a peculiar 

 Hippopotamus tusk, small and rounded, which he is inclined to 

 refer to H. minor. But Sir Eichard Owen- considers it to be simply 

 the tusk of a young H. major ; and states that these chai-acters are 

 found in the tusks of young animals of H. ampMbius. But the tusks 

 of the jaw under examination are not in the least rounded, and their 

 section is just like that of an ordinary adult tusk, and they ai-e 

 grooved in the same way. 



Assuming it then as proved, that this jaw is a jaw of H. major, 

 and is not an immature one, it seems probable that it belongs to the 

 female of H. major. It is common enough among the Omnivora, to 

 which Hipfopotamus belongs, to find the tusks much more strongly 

 developed in the male than in the female. It is true that the 

 travellers ^ who have had the best opportunities of studying Hippo- 

 p>otamus ampliihius in its native state, do not notice any very marked 

 diiference in the size of the tusks of the two sexes (except so far as 

 old males are concerned, these having enormous tusks). But there 

 is nothing unlikely in supposing that, in the case of H. major, the 

 female might have much smaller tusks than the male ; and this is 

 what the other evidence seems to point to. 



Note. — Mr. E. Lydekker, B.A., F.G.S., concurs in the author's 

 suggestion, that the relative differences in the dentition and form 

 of the jaws in the Barrington Hippopotami are really only sexual, and 

 it is therefore unnecessar}^ to figure these remains, seeing that they 

 are, in common with other Pleistocene examples, met with in this 

 country, without reasonable doubt, referable to the living species of 

 Hippoyotamus, as long since pointed out by Prof. Boyd Dawkins, 

 M.A., F.E.S. (see his Introduction to the Fossil Mammalia, PaL Soc. 

 Mon. 1866).— Edit. Geol. Mag. 



I^ IE "V I E AA7" S. 



I. — Denudation oe the Two Americas. By T. Mellard Eeade, 

 C.E., F.G.S., etc. [Presidential Address to the Liverpool 

 Geological Society, Session 1884-5.] 



IN 1876 Mr. Mellard Eeade delivered an address before the Liver- 

 pool Geological Society on the subject of " Geological Time." 

 He then introduced some calculations relating to Chemical Denuda- 

 tion, and concluded that, on an average, 143^ tons of mineral matter 

 are annually removed in solution from each square mile of the 

 surface of England and Wales. From the Danube basin he estimated 

 the annual loss by chemical denudation to be 90 tons per square 

 mile. Extending his calculations now to the larger rivers of 

 America, he concludes that from the drainage area of the Mississippi, 

 120 tons of solids in solution are removed from each square mile of 

 surface per annum. It has been estimated that the basin of this 



' " Organic Eemains," vol. iii. p. 376. 



2 "British Fossil Mammals and Jiirds," p. 403. 



3 e.g. Anderson, "Lake Ngami," p. 511. 



