410 
NATURE 
[ Sept. 2, 1886 
ively, there seems to be less parallelism between the deposits 
and forms of life of the two oceans as compared with each other, 
and less correspondence in forms of life, especially in modern 
times. Still in the earlier geological ages, as might have been 
anticipated from the imperfect development of the continents, 
the same forms of life characterise the whole ocean from Australia 
to Arctic America, and indicate a grand unity of Pacific and 
Atlantic life not equalled in Jater times,! and which speaks of 
contemporaneity rather than of what has been termed homo- 
taxis. 
We may pause here for a moment to notice some of the effects 
of Atlantic growth on modern geography. It has given us rugged 
and broken shores composed of old rocks in the north, and newer 
formations and softer features towards the south. It has given 
us marginal mountain-ridges and internal plateaus on both sides 
of the sea. It has produced certain curious and by no mears 
accidental correspondences of the eastern and western sides. 
Thus the solid basis on which the British Islands stand may be 
compared with Newfoundland and Labrador, the English 
Channel with the Gulf of St. Lawrence, the Bay of Biscay with 
the Bay of Maine, Spain with the projection of the American 
land at Cape Hatteras, the Mediterranean with the Gulf of 
Mexico. The special conditions of deposition and plication 
necessary to these results, and their bearing on the character and 
productions of the Atlantic basin, would require a volume for 
their detailed elucidation. 
Thus far our discussion has been limited almost entirely to 
physical causes and effects. If we now turn to the life-history 
of the Atlantic, we are met at the threshold with the question 
of climate, not as a thing fixed and immutable, but as changing 
from age to age in harmony with geographical mutations, and 
producing long eosmic summers and winters of alternate warmth 
and refrigeration. 
We can scarcely doubt that the close connection of the Atlantic 
and Arctic Oceans is one factor in those remarkable vicissitudes 
of climate experienced by the former, and in which the Pacific 
area has also shared in connection with the Antarctic Sea. No 
geological facts are indeed at first sight more strange and inex- 
plicable than the changes of climate in the Atlantic area, even 
in comparatively modern periods. We know that in the early 
Tertiary perpetual summer reigned as far north as the middle of 
Greenland, and that inthe Pleistocene the Arctic cold advanced, 
until an almost perennial winter prevailed, half-way to the equator. 
It is no wonder that nearly every cause available in the heavens 
and the earth has been invoked to account for these astounding 
facts. 
It will, 1 hope, meet with the approval of your veteran glacio- 
logist, Dr. Crosskey, if, neglecting most of the-e theoretical 
views, I venture to invite your attention in connection with this 
question chiefly to the old Lyellian doctrine of the modification 
of climate by geographical changes. Let us, at least, consider 
how much these are able to account for.? 
The ocean is a great equaliser of extremes of temperature. It 
does this by its great capacity for heat and by its cooling and 
heating power when passing from the solid into the liquid and 
gaseous States, and the reverse. It also acts by its mobility, its 
currents serving to convey heat to great distances, or Lo cool the 
air by the movement of cold icv waters. The land, on the other 
hand, cools or warms rapidly, and can transmit its influence to 
a distance only by the winds, and the influence so transmitted is 
rather in the nature of a disturbing than of an equalising cause. 
It follows that any change in the distribution of land and water 
must affect climate, more especially if it changes the character 
or course of the ocean currents.* 
1 Daintree and Etheridge, ‘Queensland Geology,”’ Journal of Geological 
Society, August 1872; R. Etheridge, Junior, ‘‘ Australian Fossils,’ Zxaxs. 
Phys. Soc., Edin.. 1880. 
= The late Mr. Searles V. Wood, in an able summary of the possible causes 
of the succession of cold and warm climates in the northern hemisphere, 
enumerates no fewer than seven theories which have met with more or less 
acceptance. ‘These are:— 
(1) The gradual cooling of the earth from a condition of original incan- 
descence. 
(2) Changes in the obliquity of the ecliptic. 
(3) Changes inthe position of the earth’s axis of rotation. 
(4) The effect of the precession of the equinoxes along with changes of the 
eccentricity of the earth's orbit. 
(5) Variations in theamount of heat given off by the sun. 
(6) Differences in the temperature of portions of space passed through by 
the earth. 
(7) Differences in the distribution of land and water in connection with the 
flow of cceanic currents 
3 Von Woeikc ff has very strongly put these principles in a review of 
Croll’s recent 
Science, March 1886. 
book, ‘‘Climate and Cosmology,” American Fournal of 
At the present time the North Atlantic presents some very 
peculiar, and in some respects exceptional, features, which are 
most instructive with reference to its past history. .The great 
intern: plateau of the American continent is now dry land ; 
the passage across Central America between the Atlantic and 
Pacific is blocked ; the Atlantic opens very wiclely to the north ; 
the high mass of Greenland towers in its northern part. The 
effects are that the great equatorial current running across from 
Africa and embayed in the Gulf of Mexico, is thrown north- 
ward and eastward in the Gulf Stream, acting as a hot-water 
apparatus to heat up to an exceptional degree the western coast 
of Europe. On the other hand, the cold Arctic current from 
the Polar seas is throwa to the westward, and runs down from 
Greenland past the American shore.! The pilot chart for June 
of this year shows vast fields of drift ice on the western side of 
the Atlantic as farsouth as the latitude of 40°. So far, there- 
fore, the Glacial age in that part of the Atlantic still extends ; 
this at a time when, on the eastern side of the Atlantic, the 
culture of cereals reaches in Norway beyond the Arctic Circle. 
Let us inquire into some of the details of these phenomena. 
The warm water thrown into the North Atlantic not only in- 
creases the temperature of its whole waters, but gives an excep- 
tionally mild climate to Western Europe. — Still the countervail- 
ing influence of the Arctic currents and the Greenland ice is 
sufficient to permit icebergs which creep down to the mouth of 
the Strait of Belle Isle, in the latitude of the south of England, 
to remain unmelted till the snows of a succeeding winter fall 
upon them. Now let us suppose that a subsidence of land in 
tropical America were to allow the equatorial current to pass 
through into the Pacific. The effect would at once be to reduce 
the temperature of Norway and Britain to that of Greenland 
and Labrador at present, while the latter countries would them- 
selves become colder. The northern ice, drifting down into the 
Atlantic, would not, as now, be melted rapidly by the warm 
water which it meets in the Gulf Stream. Much larger quan- 
tities of it would remain undissolved in summer, and thus an 
accumulation of permanent ice would take place, along the 
American coast at first, but probably at length even on the Euro- 
pean side. This would still further chill the atmosphere, 
glaciers would be established on all the mountains of temperate 
Europe and America,” the summer would be kept coli by melt- 
ing ice and snow, and at length all Eastern America and Europe 
might become uninhabitable, except by Arctic animals and 
plants, as far south as perhaps 40° of north latitude. This would 
be simply a return of the Glacial age. I have assumed only 
one geographical change ; but other and more complete changes 
of subsidence and elevation might take place, with effects on 
climate still more decisive ; more especially would this be the 
case if there were a considerable submergence of the land in 
temperate latitudes. 
We may suppose an opposite case. The high plateau of 
Greenland might subside, or be reduced in height, and the open- 
ings of Baffin’s Bay and the North Atlantic might be closed. 
At the same time the interior plain of America might be de- 
pressed, so that, as we know to have been the case in the Cre- 
taceous period, the warm waters of the Mexican Gulf would 
circulate as far north as the basins of the present great Ameri- 
can lakes. In these circumstances there would be an immense 
diminution of the sources of floating ice, and a correspondingly 
vast increase in the surface of warm water. The effects would 
be to enable a temperate flora to subsist in Greenland, and to 
bring all the present temperate regions of Europe and America 
into a condition of subtropical verdure. 
It is only neces-ary to add that we know that vicissitudes not 
dis-imilar from those above sketched have actually occnrred in 
comparatively recent geological times, to enable us to perceive 
that we can dispense with all other causes of change of climate, 
though admitting that some of them may have occupied a 
secondary place.? This will give us, in dealing with the distri- 
bution of life, the great advantage of not being tied up to definite 
astronomical cycles of glaciation, which may not always suit the 
geological facts, and of correlating elevation and subsidence of 
the land with changes of climate affecting living beings. It 
1 I may refer here to the admirable expositions of these effects by th: 
late Dr. Carpenter in his papers on the results of the explorations of the 
Challenger. r 
2 According tu Bonney, the west coast of Wales is about 12° above the 
average for its latitude, and if reduced to 12° below the average its moun- 
tains would have large glaciers. 
3 More especially the ingenious and elaborate arguments of Croll deserve 
consideration ; and, though I cannot agree with him in his main thesis, I 
gladly acknowledge the great utility of the work he has done. 
a 
a 
- sane 
