Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/14

x covered the whole surface of the globe, but in the course of ages, as the result of folding, it diminished in area and increased in thickness, until in late Palæozoic and early Mesozoic times it formed a vast land area which he terms Pangæa. It included practically all the present continents, which subsequently separated and moved away from one another.

Professor Wegener also adopts the view, which has been advocated in various quarters, that the position of the poles on the earth’s surface has varied from time to time so that the same land area may at different times have experienced both polar and equatorial climatic conditions. On the evidence afforded by fossils and the lithological character of the rocks as to past climates, he has endeavoured to trace the movements of the poles from Devonian times to the present day. Previous authors had suggested that the glaciation in South America, India, and Australia at the end of the Carboniferous or beginning of the Permian was due to the neighbourhood of the antarctic pole, but the difficulty had to be faced that there was no possible position of the pole that was not distant at least 70° from one of the glaciated areas. This difficulty ceases to exist if Professor Wegener is right in supposing that all of them were at that time in close proximity to one another, instead of being separated by thousands of miles of sea as at present.

One of the most interesting questions raised by Professor Wegener is the possibility of actually detecting the relative movements of land masses at the present time by instrumental means. It has been contended that a series of determinations of longitude by lunars (observations of the moon’s apparent position relatively to the stars) show a gradual increase of the west longitude of north-east Greenland relatively to Greenwich. Everything depends on the accuracy of these