Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/75

Rh biological evidence, as will be shown later, that the exchange of forms between the land areas of South America and Africa ceased in the Lower to Middle Cretaceous. This does not contradict the assumption of Passarge, that the marginal faults of South Africa were already in existence during the Jurassic, for the rift only opened gradually from the south northwards, and, moreover, the formation of the trough faults long preceded it. In Patagonia the break had as a consequence a peculiar movement of the blocks, which A. Windhausen describes in the following manner: “The new re-orientation began with regional movements of the greatest dimensions at about the middle of the Cretaceous,” when the land surface of Patagonia “was converted from an area with a pronounced slope into a field of depression which was under the influence of arid or semi-arid conditions, and was covered with gravelly desert and sandy plains.”

The Atlas mountains lying on the northern margin of the African continent, the folding of which took place chiefly in the Oligocene, but had already commenced in the Cretaceous, find no extension on the American side. This agrees with our assumption, shown in the reconstruction, that the Atlantic rift in this region had already been open a considerable time. It is indeed probable that here also it was once quite closed, but that the opening took place before