He further alleges, that in the latter case the effect of the trade winds would be to impel the heated currents of the Atlantic and Pacific Oceans further towards the North Pole, thereby causing the ice within the arctic regions to disappear, and so producing a climate sufficiently mild to admit of the existence in those regions of a fauna and flora as rich and varied as that which characterized them during any past geological period.

In the nineteenth chapter of his work he gives a diagram showing the eccentricity of the earth's orbit for 3,000,000 of years in the past, and 1,000,000 of years to come, at periods of 50,000 years apart, and tables showing those matters more in detail at intervals of 10,000 years. On looking over the diagram it will be seen that there were three principal periods in the past during which the eccentricity rose to a high value. It is to one or other of the last two that Mr. Croll assigns the geological period familiarly known as the glacial epoch, preferring, however, the later to the earlier one for reasons into which he enters at some length.

The later period consisted of two separate maxima, the earlier one being the greater of the two, and separated from the latter extreme by an interval during which the eccentricity was considerably diminished although still comparatively high, the whole period occupying 160,000 years, one-half of which would represent the united length of the cold phases in each hemisphere. Now, assuming Mr. Croll's views to be correct, the glacial epoch which was brought about by this condition of things would continuously affect each hemisphere alternately for a period of about 10,500 years, owing to the precession of the equinoxes. But the operation must have been complicated by the circumstance that, during the 160,000 years in question, there was a period of lesser eccentricity occupying some 30,000 years, during which the intensity of the cold would have been diminished in each hemisphere. It will be observed therefore that, during the period referred to, the conditions requisite, according to Mr. Croll's theory, for the production and removal of glacial conditions in the northern hemisphere would have occurred with varying intensity at alternating intervals of 10,500 years about four times, owing to the precession of the equinoxes, or, in other words, that the arctic circle would, at the intervals referred to, alternately have enjoyed atmospheric conditions which would admit of the existence of a luxuriant fauna and flora, or such as were utterly opposed to the existence of any terrestrial life.

But a glance at Mr. Croll's diagram will, I think, sufficiently show that, whilst his theory may abundantly account for an extension of pre-existing glaciated conditions in each hemisphere during periods of maximum eccentricity, there is nothing in it to lead to the conclusion that the polar ice has ever been completely removed since its first formation in mass, which, as I

contend, could only have commenced when the temperature of the surface of the ground within those regions had fallen permanently below 32° Fahr. Since my former paper was read before this society, the May number of the “Quarterly Journal of the Geological Society” has been received, and I find that the same subject which was dealt with by me in my former paper had been referred to by Professor Duncan, President of the Society, in his anniversary address. He points out that in the science of geology “strict uniformitarianism is giving way to a school which insists upon the recognition of a scientific cosmogony, which attempts the study of the mutations of the globe from the beginning, from the example of stellar and solar changes, and which considers that the principal factors in terrestrial alterations (the solar heat and the residual heat of the earth) are energies undergoing only a definite amount of reversible and more or less irreversible transformation.” And he adds that it follows, as a result of the investigations of this school, that “in the earlier geological ages, the extent and rapidity of the successive changes were greater than in the modern example, that the rigidity of the globe was less, that the internal heat and its expression in temperature at the surface were greater, and that the meteorology was such that the wear and tear of world-wide nature was larger in its annual amount.” Further on, in the same address, the learned Professor remarks, “that it must be acknowledged that a permanent increase of a few degrees of the temperature of the waters would kill off many species, and that the whole flora and fauna would cease to exist were the average heat double what it now is; that the same result would follow a moderate increase of the heat of the soil with regard to the plants; and that if the estimated amount of the heat radiated year by year, after conduction from within, relates entirely or mainly to a former much greater annual average, all being residual in its nature, the question of the possible lapse of time since the surface was cool enough to permit of life arises, and has been ably used in argument against absolute uniformitarianism.”

I ought not to make these quotations, however, without adding, that Professor Duncan does not go deeply into the question in the aspect presented in my own paper, nor can I cite his address as being altogether in support of my views; but it was satisfactory to me to find that such a speculation as that in which I ventured to indulge, was not altogether without interest or foundation in connection with geology as a practical science. My own views, put in concrete form, are these: That the arctic and antarctic regions were those which first presented climatal conditions suited to the existence of life, inasmuch as those regions must have been the first to cool down sufficiently to admit of water resting upon them in a permanently liquid condition. That, as a consequence naturally following

from the above proposition, the polar areas have become, in process of time, the great refrigerators which have supplied the cold waters now occupying the deeper parts of our oceans. That a warm climate was maintained in the polar regions—long after the heat conducted to the surface from the interior of the globe had ceased to maintain the waters above 32°—by currents of the warm water which occupied the central parts of the earth's surface; but that, so soon as the surface of the land within the polar areas had cooled sufficiently to enable snow to rest and accumulate upon the surface of the ground during ordinary winters, cold began to gain upon heat, and permit the formation and gradual accumulation of permanent ice. That ice once so formed in mass has never since been entirely removed from extreme northern and southern latitudes, but has probably extended from each towards the equator, under the operation of causes upon which I offered no opinion, but which probably were those so fully discussed by Mr. Croll. To this extent I agree with Mr. Croll, but I think he has overlooked, in connection with former climatal conditions in high latitudes, the enormous period of time which must have elapsed since the great body of water which now occupies the surface of our globe had accumulated upon it, and the effects which, during long ages, must have been produced by the passage into high latitudes of currents of water still owing its warmth to heat conducted to the surface from the interior of our globe, under the very impulses which he himself has shown to exist. It follows, moreover, that independently of the occasional extension of glacial conditions into lower latitudes, as suggested by Mr. Croll, there is reason to suppose that the climate of those latitudes will continue to suffer a gradual degradation in temperature, owing to the continuing refrigeration of the waters of the ocean, unless, indeed, this has already reached a mean, and that in the distant future the northern portions of the temperate regions may become uninhabitable, except by races like the Laplanders or the Esquimaux. Mr. Croll objects that the quantity of heat conducted from the interior to the surface of the globe is now utterly insignificant as an agent in modifying or affecting climate, but that it is still considerable cannot be doubted. The following passage from Mr. Poulett Scrope's work on Volcanos is in point on this matter:—

“In support of the hypothesis advanced at the close of the last chapter, we have, in the first place, the well-known evidence of mines and artesian wells to the fact that the temperature of the crust of the globe increases everywhere in a very rapid ratio from the surface downwards, varying from one degree in 50 to one degree in 108 feet of vertical depth, and consequently that a large amount of heat is continually in course of outward transmission from within this envelope