176 J. E. S. MOORE. 



distribution and the like, as well as the superfieial character 

 of the Halolimuic auiraals themselves, are absolutely iu accord 

 with the third hypothesis, i. e. that the Halolimnic fauna is a 

 relatively recent importation from the sea. 



But before accepting this conclusion, as the natural teaching 

 of the facts and observations which we have been discussing, 

 it is absolutely necessary to be quite sure that in the nature of 

 the country itself — that is, in the past geological history of 

 Africa — there is nothing which renders impossible the realisa- 

 tion of such a theory in fact. Now, on turning to the geological 

 aspect of the questions we have just discussed, it is apparent 

 that there is an accumulation of negative evidence drawn from 

 what is now known to geologists of the nature of the African 

 interior, which, although it does not specifically favour the 

 view of the ancient fresh-water origin of the Halolimnic forms 

 certainly renders evident a gap in the confirmation of the 

 theory of their marine origin. 



In 1852 Sir Roderick Murchison ^ advanced the hypothesis 

 that Africa, south of the Sahara, was a continent of great 

 antiquity and simplicity, the greater part of which has never 

 been changed or covered by the sea, at any rate since the age 

 of the formation of the new red sandstone. This theory has 

 appeared to be supported by the discoveries of Livingstone, 

 Burton and Speke, and Speke and Grant, and it was finally 

 re-advanced and summarised by Murchison iu 1864,^ wheu 

 he described this part of Africa as geographically unique " in 

 the long conservation of ancient terrestrial conditions. ^^ But 

 he immediately fell into the now exploded error of assuming 

 that " this impression is further supported by the con- 

 comitant absence throughout all the larger portion of this 

 vast area, i.e. south of the equator, of any of those volcanic 

 rocks which are so often associated with oscillations of the 

 terra firm a." This latter speculation is now shown to be in 

 no sense true, for there is abundant evidence of volcanic action 

 and of volcanic materials all the way from Kilimanjaro and 



' Murchison, President's Address, ' Journ. Royal Geog. Soc.,' vol. xxii, 1 852. 



* ' Jouru. Royal Geog. Soc.,' vol. xxxix, 1864, pi. xxxvii, p|). 201 — 205. 



