Köppen and WegenerReference Köppen-Wegener ¹ suggested that the main changes of climate during geological time were due to a movement of the poles relative to the main surface features of the globe, while the relatively small and quasi-periodic changes which gave rise to the glacial and interglacial epochs of the Quaternary Ice Age were due to changes in solar radiation caused by the main perturbations (the precession of the equinoxes, changes in eccentricity, etc.) of the earth’s orbit. The new hypothesis of M. Jacques BIanchard makes a movement of the poles responsible for all the changes of climate, while the movement of the pole itself is controlled by the perturbations of the orbit. The kind of movement of the North Pole envisaged by Blanchard is shown on the diagram (see Fig. 1, p. 149) which is reproduced here from his paper.

Fig. 1 Déplacements probables du Pôle Nord sur la globe, d’après les faunes

The path of the pole takes the form of a circuit, called la rotation principale, round a centre situated in north-west Greenland, on which there are five loops, called les boucles secondaires. The principal rotation is said to be controlled by the rotation of the lines of the apsides of the orbit and therefore the whole circuit is completed in 115,000 years; each loop is controlled by the precession of the equinoxes, occupying 21,000 years, so that there are approximately loops in each principal rotation. For simplicity the diagram shows 5 loops to a rotation and all the loops are drawn of the same size; but the lengths of the loops are supposed to be controlled by the changing eccentricity of the orbit—the greater the eccentricity the further the loops extend outwards. As the eccentricity varies in a period of approximately 92,000 years the lengths of successive loops increase and decrease in this period. On these lines Blanchard draws the path of the pole from 1,150,750 b.c. to a.d. 85,250; but exactly how he does it is not explained.

Now as the climate of any place is chiefly a function of its distance from the pole (latitude) it is clear that, knowing the path of the pole, the climate of any locality, at any time, can be determined. Blanchard does this for the region of the Somme in north-west France and compares the deduced changes of climate with the geological record in great detail. His conclusions can best be given in his own words:

The climates of regions outside the Somme area are then considered. There are few data and Blanchard’s discussion is very perfunctory and superficial; nevertheless he considers himself able to state:

Every theory of this nature must be judged on two considerations: first, its physical basis must be sound, and secondly, there must be agreement between the theoretical deductions and the observed facts. As to the first, one can only say that while Blanchard devotes many pages to saying why we might expect the pole to react to the several perturbations of the orbit, he nowhere gives a convincing proof that it does so react. As to the agreement between the theory and the observations, no one but an authority on the prehistory of the Somme area could criticize the many pages of detailed discussion which Blanchard gives to this aspect of the problem. But even if we accept Blanchard’s own conclusions quoted above, we must not forget that other compotent workers in this field Reference Zeuner ² have shown equal skill in fitting the same evidence into Milankovitch’s theory which, while being based on practically the same astronomical data, gives entirely different results both in time and space.