Note 22 — Chapter IV

Nothing is said about Cape Horn; as America in relation to Asia is an island. It is also, perhaps, unnecessary to repeat that both the rate and the centre are hypothetical—either or both may or may not be correct. That which is not hypothetical is the approximation to an equability of rate in the case of continents. It is difficult to conceive any such conditions, as those which deferred the occupancy of islands like Madagascar and Iceland, by emigrants from Africa or Greenland, for an indefinite period, keeping one part of Africa or Greenland empty whilst another was full. Hence, the equability in question is a mere result of the absence, on continents, of any conditions capable of arresting it for an indefinite period. The extent to which it may be interfered with by other causes is no part of the present question.