The history of our globe during the deposition of the CHALK FORMATION, and the changes therewith connected, have now to be considered. By whatever causes effected—from whatever sources derived the materials—the line of demarkation is here complete. The sands of Africa, suddenly converted into or drifted over by the snows of the Alps, would not present a greater diversity of outline than is the transition to the geologist, when for the first time he steps into a chalk district, and marks the obvious contrast with all the surrounding scenery. From Gloucester into Wiltshire we pass, as it were, into a new zone of latitude. The details contained in the two last chapters are in strict conformity with the laws of nature: the animals connected with the epoch possessed functions of life and an external adaptation of things suited to each other. Similar arrangements exist at present under nearly similar circumstances: the tropical animals bear a close affinity to the extinct races; and show that, however nature may contrive to display her exhaustless powers of invention in her forms of living creatures, she still conforms to a type, and has her limits of divergence. The past and the present so agree in all essential points as clearly to demonstrate a wise and controlling agency, a measure of enjoyment combined with an adjustment of figure, which, though approaching the marvelous, has resulted from design and the profoundest intelligence. Accordingly, the symptoms of the change we now witness are cotemporaneous. With the cretaceous system are introduced new mineral conditions, and along with these there are new forms of existence. The animals of the chalk and oolite periods are essentially different—still generically shading, indeed, into each other—but so differing in species, and the appearance for the first time of new creations, as again to announce to us that we tread on sacred ground, and witness in its arrangement and contents the direct agency of Omnipotence. We can form no opinion, no notion whatever, in these changes, of the _modus operandi_. We remark simply the effects; and science, amidst all its otherwise barren and useless details, then achieves its loftiest purposes when it thus traces the footsteps and actings of the Great First Cause.