CHAP. XIV.] 
THE NEOTROPICAL REGION. 
81 
periods of union with the northern continent. The latest 
important separation took place by the submergence of parts 
of Nicaragua and Honduras, and this separation probably con- 
tinued throughout much of the Miocene and Pliocene periods ; 
but some time previous to the coming on of the glacial epoch, the 
union between the two continents took place which has con- 
tinued to our day. Earlier submergences of the isthmus of 
Panama probably occurred, isolating Costa Kica and Yeragua, 
which then may have had a greater extension, and have thus 
been able to develope their rich and peculiar fauna. 
The isthmus of Tehuantepec, at the south of Mexico, may, 
probably, also have been submerged ; thus isolating Guatemala 
and Yucatan, and leading to the specialization of some of the 
peculiar forms that now characterise those countries and Mexico. 
The West Indian Islands have been long isolated and have 
varied much in extent. Originally, they probably formed part 
of Central America, and may have been united with Yucatan 
and Honduras in one extensive tropical land. But their sepa- 
ration from the continent took place at a remote period, and 
they have since been broken up into numerous islands, which 
have probably undergone much submergence in recent times. 
This has led to that poverty of the higher forms of life, com- 
bined with the remarkable speciality, which now characterises 
them ; while their fauna still preserves a sufficient resemblance 
to that of Central America to indicate its origin. 
The great continent of South America, as far as we can judge 
from the remarkable characteristics of its fauna and the Vast 
depths of the oceans east and west of it, has not during Tertiary, 
and probably not even during Secondary times, been united with 
any other continent, except through the intervention of North 
America. During some part of the Secondary epoch it probably 
received the ancestral forms of its Edentates and Rodents, at a 
time when these were among the highest types of Mammalia 
on the globe. It appears to have remained long isolated, and to 
have already greatly developed these groups of animals, before it 
received, in early Tertiary times, the ancestors of its marmosets 
and monkeys, and, perhaps also, some of its peculiar forms of 
VOL. II. o 
