the miocene period, like Madeira, Porto Santo, and the Desertas, constituting the small Madeiran Archipelago, we might have expected to discover a difference in the species of land-shells, not only when Ireland was compared to England, but when different islands of the Hebrides were contrasted one with another, and each of them with England. It would not, however, be necessary, in order to effect the complete fusion of the animals and plants which we witness, to assume that all parts of the area formed continuous land at one and the same moment of time, but merely that the several portions were so joined within the post-pliocene era as to allow the animals and plants to migrate freely in succession from one district to another.
Southernmost Extent of Erratics in England.
In reference to that portion of the south of England which is marked by diagonal lines in the map at p. 260, the theory of its having been an area of dry land during the period of great submergence and floating-ice does not depend merely on negative evidence, such as the absence of the northern drift or boulder clay on its surface; but we have also, in favour of the same conclusion, the remarkable fact of the presence of erratic blocks on the southern coast of Sussex, implying the existence there of an ancient coast-line at a period when the cold must have been at its height.
These blocks are to be seen in greatest number at Pagham and Selsea, fifteen miles south of Chichester, in lat. 50° 40' N.
They consist of fragments of granite, syenite, and greenstone, as well as of Devonian and Silurian rocks, some of them of large size. I measured one of granite at Pagham, twenty-seven feet in circumference. They are not of northern origin, but must have come from the coast of Nor-
