DARWIN ON GALAPAGOS FAUNA 
297 
hand, Darwin’s* remark that he noticed a few fragments of 
granite curiously glazed and altered by heat among the ejecta- 
menta, would seem to imply that the bases of the craters are 
composed of older forms of eruptive rocks. This supposition 
is strengthened by an observation made by Professor Suess,f 
that on the whole of the Pacific coast of America only a single 
mountain range comes to an abrupt termination on the Pacific 
coast, namely, the Central American continuation of the An¬ 
tillean Cordillera, and that precisely at the point where we 
might imagine the arcuate prolongation of this chain to meet 
the principal South American mountains lie the volcanic Gala¬ 
pagos islands. At any rate, as Dr. Blanford $ has pointed 
out, the rocks of an island may he entirely volcanic, although 
the island may nevertheless be a remnant of a continental 
mass. Except that some- of the craters have their southern 
faces broken down, which may be due to some other cause 
than that suggested by Darwin, the Galapagos islands could 
just as well represent the mountain tops of sunken land as 
the summits of originally submarine volcanoes. Neither of 
these two theories is supported by strong geological evidence. 
No one was more impressed by this fact than Darwin himself, 
and he bases his theory of the origin of the Galapagos fauna 
and flora almost entirely on the nature, composition and dis¬ 
tribution of the animals and plants he found on the islands. 
His conclusions were that all the animals and plants must be 
derived from accidental transport by sea-currents or by birds, 
except for a few recent immigrants which were introduced by 
man. 
The natural history of the islands, as Darwin truly remarks, 
is eminently curious and well deserves attention. Of terres¬ 
trial mammals, he says, there is only one which must be con¬ 
sidered as indigenous, namely a mouse (Mus galapagoensis). 
A rat also is sufficiently distinct from the common kind to have 
been named and described, “ but,” continues Mr. Darwin, 
“ as it belongs to the Old World division of the family, and as 
this island had been frequented by ships for the last hundred 
and fifty years, I can hardly doubt that this rat is merely a 
* DarwiD, C., “ Journal of Researches,” pp. 270—271. 
t Suess, E., “Das Antlitz der Erde,” II., p. 263. 
f Blanford, W. T., “Anniversary Address,” p. 34. 
