CHAP. XIX.] 
THE MADAGASCAR GROUP. 
397 
very deep sea — much deeper than that which divides Mada- 
gascar from Africa, and we have therefore no reason to imagine 
their former union. But they would nevertheless greatly facili- 
tate the introduction of Indian birds into the Mascarene Islands 
and Madagascar; and these facilities existing, such an immigra- 
tion would be sure to take place, just as surely as American birds 
have entered the Galapagos and Juan Fernandez, as European 
birds now reach the Azores, and as Australian birds reach such 
a distant island as New Zealand. This would take place the 
more certainly because the Indian Ocean is a region of violent 
periodical storms at the changes of the monsoons, and we have 
seen in the case of the Azores and Bermuda how important a 
factor this is in determining the transport of birds across the 
ocean. 
Mr. Darwin’s theory of the formation of atolls is now almost 
universally accepted as the true one, and this theory implies 
that the areas in question are still, or have very recently been, 
subsiding. The final disappearance of these now sunken islands 
does not, therefore, in all probability, date back to a very re- 
mote epoch ; and this exactly accords with the fact that some 
of the birds, as well as the fruit-bats of the genus Pteropus, are 
very closely allied to Indian species, if not actually identical, 
others being distinct species of the same genera. The fact that 
not one closely-allied species or even genus of Indian or Malayan 
mammals is found in Madagascar, sufficiently proves that it is 
no land-connection that has brought about this small infusion of 
Indian birds and bats ; while we have sufficiently shown, that, 
when we go back to remote geological times no land-connection 
in this direction was necessary to explain the phenomena of the 
distribution of the Lemurs and Insectivora. A land-connection 
with some continent was undoubtedly necessary, or there would 
have been no mammalia at all in Madagascar ; and the nature 
of its fauna on the whole, no less than the moderate depth of 
the intervening strait and the comparative approximation of the 
opposite shores, clearly indicate that the connection was with 
Africa. 
Concluding remarks on “ Lemuria .” — I have gone into this 
question in some detail, because Dr. Hartlaub’s criticism on my 
