Origin of Species Variorum

→ is extremely severe, and lasts for a great length of time. 1869

of which the most important, as Sir C. Lyell has shown, is the relative position of the land and water. 1872

→ in relation to our present subject, 1869

OMIT 1872

→ arrived 1869

for us, arrived 1872

→ have, as we shall immediately see, a most important bearing 1869

throws so much light 1872

→ will 1869

am strongly inclined to trust in it; but I will 1872

↑ 8 blocks not present in 1869 1872; present in 1859 1860 1861 1866

We do not know that the Glacial epoch was strictly simultaneous at these several far distant points on opposite sides of the world. But we have good evidence in almost every case, that the epoch was included within the latest geological period. We have, also, excellent evidence, that it endured for an enormous time, as measured by years, at each point. The cold may have come on, or have ceased, earlier at one point of the globe than at another, but seeing that it endured for long at each, and that it was contemporaneous in a geological sense, it seems to me probable that it was, during a part at least of the period, actually simultaneous throughout the world. Without some distinct evidence to the contrary, we may at least admit as probable that the glacial action was simultaneous on the eastern and western sides of North America, in the Cordillera under the equator and under the warmer temperate zones, and on both sides of the southern extremity of the continent. If this be admitted, it is difficult to avoid believing that the temperature of the whole world was at this period simultaneously cooler. But it would suffice for my purpose, if the temperature was at the same time lower along certain broad belts of longitude. On this view of the whole world, or at least of broad longitudinal belts, having been simultaneously colder from pole to pole, much light can be thrown on the present distribution of identical and allied species.

→ besides many closely allied species, between 1869 1872

between 1859 1860 1861 1866

→ North America and Europe, 1869 1872

Europe, 1859 1860 1861 1866

→ areas in opposite hemispheres are from each other. 1869 1872

two points are; and there are many closely allied species. 1859 1860 1861 1866

→ temperate European, some Antarctic, and some Andean 1869 1872

European 1859 1860 1861 1866

→ genera 1859 1860 1861 1869 1872

temperate, some antarctic, and some Andean genera 1866

→ countries. 1859 1860 1861 1869 1872

countries; and I have been informed that Agassiz has lately discovered plain marks of glacial action on these same mountains. 1866

certain contingencies, →is extremely severe, and lasts for a great length of time. Mr. Croll believes that the last great Glacial period occurred about 240,000 years ago, and endured with slight alterations of climate for about 160,000 years. With respect to more ancient Glacial periods, several geologists are convinced from direct evidence that such occurred during the Miocene and Eocene formations, not to mention still more ancient formations. But →in relation to our present subject, the most important result →arrived at by Mr.

Croll,

Croll

is,

that whenever the northern hemisphere passes through a cold period, the temperature of the southern hemisphere is actually raised, with the winters rendered much milder, chiefly through changes in the direction of the ocean-currents. So conversely it

will be

with the northern hemisphere,

whilst

when

the southern passes through a glacial period.

This

These

conclusion

conclusions

→have, as we shall immediately see, a most important bearing on geographical

distribution

distribution;

that

but

I →will first give the facts, which demand an explanation. ↑

America,

South America,

Dr. Hooker has shown that →besides many closely allied species, between forty and fifty of the flowering plants of Tierra del Fuego, forming no inconsiderable part of its scanty flora, are common to →North America and Europe, enormously remote as these →areas in opposite hemispheres are from each other. On the lofty mountains of equatorial America a host of peculiar species belonging to European genera occur. On the

highest

Organ

mountains of Brazil, some few →temperate European, some Antarctic, and some Andean →genera were found by Gardner, which do not exist in the

wide

low

intervening hot →countries.

So on

the Silla of

Caraccas,

Caraccas

the illustrious Humboldt long ago found species

belong- ing

belonging

to genera characteristic of the

Cordillera.

In Africa, several forms characteristic of Europe and