Origin of Species Variorum

→ at one time 1872

formerly 1869

→ According to 1872

It follows from 1869

→ and these at long intervals are extremely severe, 1872

but that at much longer intervals the cold, 1869

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

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

→ OMIT 1872

in relation to our present subject, 1869

→ for us, arrived 1872

arrived 1869

→ throws so much light 1872

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

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

will 1869

↑ 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

extended all round the northern and southern hemispheres— from the period having been in a geological sense recent in both hemispheres— from its having lasted in both during a great length of time, as may be inferred from the amount of work effected— and lastly from glaciers having recently descended to a low level along the whole line of the Cordillera, it →at one time appeared to me that we could not avoid the conclusion that the temperature of the whole world had been simultaneously lowered during the Glacial period. But now Mr. Croll, in a series of admirable memoirs, has attempted to show that a glacial condition of climate is the result of various physical causes, brought into operation by an increase in the

excentricity

eccentricity

of the

earths

earth's

orbit. All these causes tend towards the same end; but the most powerful appears to be the

influence

indirect influence

of the

excentricity

eccentricity

of the orbit upon oceanic currents. →According to Mr.

Crolls

Croll,

researches, that

....

cold periods regularly recur every ten or fifteen thousand years; →and these at long intervals are extremely severe, owing to certain contingencies, →of which the most important, as Sir C. Lyell has shown, is the relative position of the land and water. 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 →OMIT the most important result →for us, 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,

when

whilst

the southern passes through a glacial period.

These

This

conclusions

conclusion

→throws so much light on geographical

distribution;

distribution

but

that

I →am strongly inclined to trust in it; 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