The great elevation of the continents which closed the Cretaceous was followed by a partial and unequal subsidence, affecting principally the more southern parts of the land of the northern hemisphere. Thus, a wide sea area stretched across all the south of Europe and Asia, and separated the northern part of North America from what of land existed in the southern hemisphere. This is the age of the great Nummulitic Limestones of Europe, Africa, and Asia, and the Orbitoidal Limestones of North America. The names are derived from the prevalence of certain forms of those humble shell-bearing protozoa which we first met with in the Laurentian, and which we have found to be instrumental in building up the chalk, the _Foraminifera_ of zoologists. (Fig. p. 243.) But in the Eocene the species of the chalk were replaced by certain broad flat forms, the appearance of which is expressed by the term nummulite, or money-stone; the rock appearing to be made up of fossils, somewhat resembling shillings, sixpences, or three-penny pieces, according to the size of the shells, each of which includes a vast number of small concentric chambers, which during life were filled with the soft jelly of the animal. The nummulite limestone was undoubtedly oceanic, and the other shells contained in it are marine species. After what we have already seen we do not need this limestone to convince us of the continent-building powers of the oceanic protozoa; but the distribution of these limestones, and the elevation which they attain, furnish the most striking proofs that we can imagine of the changes which the earth's crust has undergone in times geologically modern, and also of the extreme newness of man and his works. Large portions of those countries which constitute the earliest seats of man in Southern Europe, Northern Africa, and Western and Southern Asia, are built upon the old nummulitic sea-bottom. The Egyptians and many other ancient nations quarried it for their oldest buildings. In some of these regions it attains a thickness of several thousand feet, evidencing a lapse of time in its accumulation equal to that implied in the chalk itself. In the Swiss Alps it reaches a height above the sea of 10,000 feet, and it enters largely into the structure of the Carpathians and Pyrenees. In Thibet it has been observed at an elevation of 16,500 feet above the sea. Thus we learn that at a time no more geologically remote then the Eocene Tertiary, lands now of this great elevation were in the bottom of the deep sea; and this not merely for a little time, but during a time sufficient for the slow accumulation of hundreds of feet of rock, made up of the shells of successive generations of animals. If geology presented to us no other revelation then this one fact, it would alone constitute one of the most stupendous pictures in physical geography which could be presented to the imagination. I beg leave here to present to the