CHAP. XIV.] 
ST. HELENA. 
291 
the same direction, so that any transmission of insects by their 
means must almost certainly be from South Africa. Now there 
is undoubtedly a South African element in the insect-fauna, but 
there is no less clearly a European, or at least a north-temperate 
element, and this is very difficult to account for by causes now 
in action. But when we consider that this northern element is 
chiefly represented by remote generic affinity, and has therefore 
all the signs of great antiquity, we find a possible means of 
accounting for it. We have seen that during early Tertiary 
times an almost tropical climate extended far into the northern 
hemisphere, and a temperate climate to the Arctic regions. 
But if at this time (as is not improbable) the Antarctic regions 
were as much ice-clad as they are now, it is certain that an 
enormous change must have been produced in the winds. In- 
stead of a great difference of temperature between each pole 
and the equator, the difference would be mainly between one 
hemisphere and the other, and this might so disturb the trade 
winds as to bring St. Helena within the south temperate region 
of storms — a position corresponding to that of the Azores and 
Madeira in the North Atlantic, and thus subject it to violent 
gales from all points of the compass. At this remote epoch the 
mountains of equatorial Africa may have been more extensive 
than they are now, and may have served as intermediate stations 
by which some northern insects may have migrated to the 
southern hemisphere. 
We must remember also, that these peculiar forms are said 
to be northern only because their nearest allies are now found 
in the North Atlantic islands and Southern Europe ; but it is 
not at all improbable that they are really widespread Miocene 
types, which have been preserved mainly in favourable insular 
stations. They may therefore have originally reached St. 
Helena from Southern Africa, or from some of the Atlantic 
islands, and may have been conveyed by oceanic currents as 
well as by winds . 1 This is the more probable, as a large 
1 On Petermann’s map of Africa, in the new edition of Stieler' s Hand- 
Atlas (1879), the Island of Ascension is shown as seated on a much larger 
and shallower submarine bank than St. Helena. The 1,000 fathom line 
round Ascension encloses an oval space 170 miles long by 70 wide, and 
