In land animals a high degree of temperature, depending on latitude, appears to have exercised a favourable influence on the genetic development of organization. Thus the small and slender form of our lizards expands in the south into the colossal, unwieldy, and mail-clad body of the formidable crocodile. In the huge cats of Africa and America, the tiger, lion, and jaguar, we find, repeated on a larger scale, the form of one of the smallest of our domestic animals. But if we penetrate into the recesses of the earth, and search the tombs of plants and animals, the fossil remains thus brought to light not only manifest a distribution of forms at variance with the present climates, but they also reveal colossal structures, which exhibit as marked a contrast with the small types that now surround us, as does the simple yet dignified heroism of the ancient Greeks, when compared with what is recognized at the present day as “greatness of character.” If the temperature of the earth has undergone considerable, perhaps periodically recurring changes, and, if even the relations between sea and land, and the height and pressure of the atmospheric ocean[84], have not always been the same, then the physiognomy of nature, and the magnitude and forms of organic bodies, must also have been subject to many variations. Enormous Pachydermata, elephantine Mastodons, Owen’s Mylodon robustus, and the Colossochelys,[JA] a land tortoise upwards of six feet in height, once inhabited forests of colossal Lepidodendra, cactus-like Stigmariæ, and numerous genera of Cycadeæ. Unable accurately to delineate the physiognomy of our aging and altering planet according to its present features, I will only attempt to bring prominently forward those characteristics which specially appertain to each individual group of plants. Notwithstanding all the richness and adaptability of our language, the attempt to designate in words, that which, in fact, appertains only to the imitative art of the painter, is always fraught with difficulty. I would also wish to avoid that wearying effect which is almost unavoidably inseparable from a long enumeration of individual forms.