In land animals the higher temperatures of the low latitudes appear to have favoured organic development. The small and slender form of our lizards is exchanged in the south for the gigantic, heavy, and cuirassed bodies of crocodiles. In the formidable tiger, lion, and jaguar, we see repeated, on a larger scale, the form of the common cat, one of the smallest of our domestic animals. If we penetrate into the interior of the earth, and search the cemeteries in which the plants and animals of the ancient world lie entombed, the fossil remains which we discover not only announce a distribution inconsistent with our present climates,--they also disclose to us gigantic forms that contrast no less with those which now surround us, than does the simple heroism of the Greeks with the character of human greatness in modern times. Has the temperature of our planet undergone considerable changes,--possibly of periodical recurrence? If the proportion between land and sea, and even the height of the aerial ocean and its pressure,[14] have not always been the same, the physiognomy of nature, and the dimensions and forms of organised beings, must also have been subjected to various alterations. Huge Pachydermata, Mastodons, Owen’s Mylodon robustus, and the Colossochelys, a land-tortoise above six feet high, have existed, and in the vegetable kingdom there have been forests composed of gigantic Lepidodendra, cactus-like Stigmarias, and numerous kinds of Cycadeæ. Unable to depict fully according to its present features the physiognomy of our planet in this its later age, I will only venture to attempt to indicate the characters which principally distinguish those vegetable groups which appear to me to be most strongly marked by physiognomic differences. However favoured by the richness and flexibility of our native language, it is still an arduous and hazardous undertaking when we attempt to trace in words that which belongs rather to the imitative art of the painter. I feel also the necessity of avoiding as much as possible the wearisome impression almost inseparable from all lengthened enumerations.