Fig. 10—A Fossil Shell (Pecten murrayanus, Tate).
Of Oligocene to Lower Pliocene Age in Southern Australia; closely allied to, if not identical with, a species living off the coast of Queensland. About nat. size.
(F.C. Coll.)
From the above evidence we may say that:—
2.—Fossils teach us that in Former Times the Climate of certain parts of the earth’s surface was Different from that now existing.
Fossils as Guides to Age of Strata.—
In passing from fossil deposits of fairly recent origin to those of older date, we find the proportion of living species gradually diminish, being replaced by forms now extinct. After this the genera themselves are replaced by more ancient types, and if we penetrate still deeper into the series of geological strata, even families and orders of animals and plants give place to others entirely unknown at the present day.
From this we conclude that:—
3.—Fossil Types, or Guide Fossils, are of great value in indicating the Relative Age of Geological Formations.