MICHIGAN ACADEMY OF SCIENCE. 
127 
reference to the charts that the initial difficulty to be encountered by 
land animals starting to migrate north from the mainland or from 
Trinidad is a depth of 2,21b feet. Further north, about the middle of 
the chain, we have depths of S.07G feet, 7,392 and G,4G<S, diminishing 
again still further north to 2,700 and 2,088. From 0,000 1<> 8,000 feet 
therefore is an inside estimate of the amount of vertical movement 
indicated. 
Falconer's resume of the subject has already been mentioned. It 
is worth emphasizing that the facts of animal distribution in these 
islands have led to exactly the same conclusion that was reached by 
Hilgard* in the study of the “Grand Gulf” formation along the shores 
of the Gulf of Mexico, namely, that up to the Glacial Epoch, ( not neces- 
sarily ending at the beginning of that epoch) there was such an eleva- 
tion of the northern and eastern borders of the Caribbean Sea that the 
•waters of the Gulf were separated from those of the ocean and became 
brackish or even fresh from the preponderance of the inflow from the 
land. It seems as though this combination of indirect geological and 
direct biological inference ought to be very reliable, and it is interesting 
to notice that the figures involved, 6,000 to 8,000 feet, while higher than 
those obtained for heavily glaciated North America, correspond very 
well with others that we have for South America and Africa. The 
depths between the islands must be increased by whatever sedimenta- 
tion has occurred, so that they by no means form a maximum limit of 
the drowning. The natural presumption is that these submerged places 
were well above sea level to begin with, and that now, submerged, the 
connecting ridges have been built up by sedimentation. Orogenic move- 
ments, however, must be borne in mind, especially in this region. 
SOUTH AMERICA, AFRICA AND INDIA. 
As bearing upon the climate and altitude of tropical South America, 
Africa and India in the Glacial Epoch, I will quote DarwiiTsf summary 
of a discussion of related facts. 
“From the foregoing facts, namely the presence of temperate forms 
on the highlands across the whole, of equatorial Africa and along the 
Peninsula of India to Ceylon and the Malay Archipelago, and in a less 
well-marked manner across the wide expanse of tropical South America, 
it appears almost certain that at some former period, no doubt during 
the most severe part of a Glacial period, the lowlands of these great 
continents were everywhere tenanted under the equator by a consider- 
able number of temperate forms. At this period the equatorial climate 
at the level of the sea was probably about 1 lie same with that now ex- 
perienced at the height of from five to six thousand feet under the same 
latitude, or perhaps even rather cooler. During this, the coldest period, 
the lowlands under the equator must have been clothed with a mingled 
tropical and temperate vegetation, like that described by Hooker as 
growing luxuriantly at the height of from four to five thousand feet 
on the lower slopes of the Himalaya, but with perhaps a still greater 
preponderance of temperate forms/’ 
In view of the other evidence for elevation at the time that Darwin 
*Hilgard, E. W., “On the Geological History of the Gulf of Mexico." Am. Jour. Sci. and Arts, Ser. 
3, vol. ii, 1871, pp. 391-404. 
t Darwin, Charles, “Origin of Species,” Levant Ed. p. 371. 
