In Part IV of this paper the theory that the earth has continuously cooled down from a former molten state was shown to lead to limitations of temperature and to a distribution of rock-types at moderate depths which, taken together, made it impossible for igneous activity to have taken place as we know it to have done. It was argued that this conclusion definitely proved the theory to be wrong. Now, instead of deducing the distribution of rock-types in depth from their radioactive contents, the method of attack will be reversed and an attempt will be made to determine the downward distribution independently, so that the radioactive effects may be deduced without reference to any limiting hypothesis of a steadily cooling earth.

The northern mountain range of schistose rocks of the Island of Trinidad reaches an altitude of 3,012 feet in Mount Tucutche and consists of a wild and tumbled mass of ridges with deep intervening valleys clothed from top to bottom with tropical vegetation, the abode of a practically undisturbed fauna and flora. Westwards the range is continued in the rugged and precipitous islands of Monos, Huevos, and Chacacare between which are the Bocas through which ships pass in entering the Gulf of Paria from the north. The entrance to the Gulf is famous for its scenic beauty. North-eastwards the schist-range reappears in the island of Tobago, but no limestones are reported to occur among the rocks there. Westwards the high range of schistose mountains continues along the northern coast of a great part of Venezuela,4 and over 800 miles further west at Santa Marta in the Kepublic of Colombia I have seen a series of schists very similar in lithology to those that form the northern range of Trinidad.