In the third edition of his Text-Book of Geology, Sir Archibald Geikie has discussed the question whether fossils can be wholly depended upon to indicate the age of rocks when similar or representative species are found in areas wide apart. Thus he tells us (p. 665) that in Bohemia and Russia some of the most characteristic Upper Silurian organisms are found beneath strata replete with Lower Silurian life. Again, speaking of the close of the Silurian period, he says (p. 760): “There is every reason to believe that for a long time the marine sedimentation of Upper Silurian type continued to prevail in some areas, while the probably lacustrine type of the Old Red Sandstone had already been established in others.” He also tells us (p. 828) that “In the West of Scotland there occur among the red sandstones (some of which contain Old Red Sandstone fishes) bands of limestone full of true Carboniferous Limestone corals and brachiopods.” Again (p. 665), he draws our attention to the statement that “In Australia a flora with Jurassic affinities and a Carboniferous Limestone fauna were contemporaneous” while we may conclude our extracts by one which says: “At the present day the higher fauna of Australia is more nearly akin to that which flourished in Europe far back in Mesozoic time, than to the living fauna of any other region of the globe.”