In the following Table the temperatures according to latitudes are represented (1) for the whole Northern Hemisphere, (2) for the warmest band of water up the Atlantic', (3) the difference of these or the warming influence exerted by the sea-currents and winds.

As already observed the temperatures, even in the warm North Atlantic band, are not high enough to suit the case of the Coral growths in Palæozoic and Mesozoic ages, which demand in lat. 60° about 34°, in addition to the average temperature, or 18° above the highest observed temperature.

To meet this necessity we may suppose a more effective distribution of the equatorial temperature into the basins of the North. We may further suppose, for the sake of calculation, the average result

1 From Dove's Maps of Temperature.

for each zone of latitude to be an increase of warmth proportioned to the difference of area between that zone and the equatorial zone. On this supposition the following calculation is made1.

The addition to mean temperature in lat. 60° being taken at 30°, the scale of augmentations for the whole series of latitudes will be nearly as in Col. I., and, the equatorial temperature remaining the same, the temperature for each latitude up to 70° will be as in Col. II.

These temperatures would meet the geological requirement; but it seems very doubtful whether there is enough of probability about the hypotheses on which they are founded, to meet the two objections which follow. 1. The augmentation, here attri

1 The formula is merely this. Augmentation = A (rad. — cos. lat.).

buted to a considerable part at least of the hemisphere, is twice as great in amount as in the most favourable example now to be found on any part of the globe. 2. The average temperature of the whole area affected must be augmented by about 13o. Though neither of these conditions may be accepted as very probable, we can hardly avoid believing the varying distribution of land and water to be an important element in a just explanation of ancient high climate in northern zones.

There is indeed a further consideration which deserves much attention. One characteristic of the climates not very far from the equator is the small range of the annual temperature, only a few degrees being the full amount of vicissitude in this respect through the year. Some weight must be allowed to this in forming our scale of required additional temperature; perhaps a considerable weight. Under the conditions assumed in the last calculation the whole of the oceanic temperatures would become remarkable for very small variations from one part of the year to another; and thus one characteristic requisite in the life of the plants and animals of the warm regions being perfectly fulfilled, it seems very probable that so high an average temperature as that assumed might not be required. If we allow full force to this idea, and conceive the equatorial tem

perature to be lowered (as it would be) by an effective distribution of part of its warmth by currents directed toward the poles, the difficulty would be much reduced.

For those who are not satisfied with the proba→ bility of the explanation just examined, another hypothesis is ready, the displacement of the axis of the earth. Though this is refused by the proper authorities, the astronomers, it may be worth while to mention that the centre of gravity of the earth cannot be regarded as having been always absolutely fixed when we remember the irregular distribution of the axes of elevation of different periods, the very considerable mass of the elevated mountainchains, and the great amount of subsidence by which the areas of deposition have been affected at different times. But if the centre of gravity of the earth be allowed to be thus inconstant in position, the axis of rotation must be subject to change from the same cause. Such minute variations, however, would be of small efficacy in regard to the matter in hand, if we are to judge by the actual distribution of the masses of elevated land, and the direction of the depths of the sea. Even if we could place an extra load on one meridian between the pole and the equator, and thus cause an angular deviation of the axis, this is a process requiring long perseverance

and many repetitions in the economy of nature to produce a sensible effect'.

Passing without remark conjectures regarding the limits of the precession of the equinoxes, and the obliquity of the ecliptic, and estimates of the variation of the diameter of the earth's orbit, by which it has been attempted to meet the difficulties of ancient geological climate, a few words may be added regarding one speculation which has justly received more serious consideration. The interior temperature of the earth is observed to augment sensibly as we descend; the figure of the earth indicates original fluidity; the lowest rocks agree with the opinion that great heat has been an essential agent in giving to them their present appearance. The earth is hotter within than at the surface; receives a current of heat from the interior, and dissipates it into space; grows cooler, and has been always growing cooler, from the earliest times. Why not suppose the greater surface-heat of early times to have been caused by the then greater and nearer influence of the interior much heated masses? The influence of such a flow of heat outward to all parts of the surface, independent of latitude, is exactly of such a kind

1 Col. Sir H. James has attributed a great effect to this cause, Athenæum, Sept. 1860. Remarks have followed by Professor Airy, Professor Jukes, and Professor Hennessy, which agree with the views expressed in this work.

R. L.

M