I last passed through this wondrous gallery at the time when the attraction of the Great Exhibition had filled London with curious visitors from all parts of the empire; and a group of intelligent mechanics, fresh from some manufacturing town of the midland counties, were sauntering on through its chambers immediately before me. They stood amazed beneath the dragons of the Oolite and Lias; and, with more than the admiration and wonder of the disciples of old when contemplating the huge stones of the Temple, they turned to say, in almost the old words, "Lo! master, what manner of great beasts are these?" "These are," I replied, "the sea monsters and creeping things of the second great period of organic existence." The reply seemed satisfactory, and we passed on together to the terminal apartments of the range appropriated to the Tertiary organisms. And there, before the enormous mammals, the mechanics again stood in wonder, and turned to inquire. Anticipating the query, I said, "And these are the huge beasts of the earth, and the cattle of the third great period of organic existence; and yonder, in the same apartment, you see, but at its further end, is the famous fossil man of Guadaloupe, locked up by the petrifactive agencies in a slab of limestone." The mechanics again seemed satisfied. And, of course, had I encountered them in the first chamber of the suite, and had they questioned me respecting the organisms with which _it_ is occupied, I would have told them that they were the remains of the herbs and trees of the _first_ great period of organic existence. But in the chamber of the mammals we parted, and I saw them no more.