Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.3)

ADDENDA. 611 are found in the southern hemisphere, and likewise of some mammaUa and of birds. With respect to the parrot of the Strait of Magellan, Mac- quarrie Island in lat. 55° S. and long 160° E. offers an analogous instance, in possessing a species of this genus. I am, however, now enabled to bring forward a more important observation, as directly bearing on the evidence by which geologists have chiefly judged of the climate of ancient Europe, namely, on the character of the marine productions of the south- ern hemisphere. In my journal I have remarked that the southern seas teem with life, under innumerable forms ; and the truth of this remark is amply attested by the vast herds of great unwieldy seals with which the shores of Patagonia, the Falkland and the Antarctic islands, were, ac- cording to the narratives of all the early navigators, almost covered. Having mentioned these facts to Mr. George B. Sowerby, he informs me, that the shells of the southern part of the southern hemisphere have some affinity in general character with those of the intertropical seas, or rather that they are of much larger size and of more vigorous growth than the analogous species (excepting the chitons of California) under correspond- ing zones in the northern hemisphere. Thus the immense size of the Patellae, Fissurellae, Chitons, and Barnacles of the Strait of Magellan, and the large size of the former at the Cape of Good Hope, may be taken as instances. On the east coast of South America (in lat. 39°) three species of Oliva (one of large size), a Voluta (and perhaps a second species), and a Terebra, are amongst the most abundant shells on the mud-banks of Bahia Blanca. Another species of Voluta is found as far south as 45°, and there is some reason to believe, even much further. Oliva, Voluta, and Terebra are amongst the best-characterized tropical forms, that is, both the individuals and species of these genera are extremely abundant in the intertropical seas, whilst they are very rare, or do not exist, on the shores of temperate countries. It is doubtful even if one small species of these three genera, an Oliva, inhabits the southern shores of Europe ; whilst in a higher latitude, on the coast of South America, species of all three are the most abundant kinds. At Bahia Blanca many of these shells are embedded in gravel, and have been raised above the level of the sea. Now let us suppose that the climate of South America and of the surrounding seas were to undergo some change, so as to become in every respect like that of Europe ; it can, I think, scarcely be doubted, that the shells of the abovementioned genera would gradually become extinct, and be replaced by others better adapted to the new climate. What, then, would a geologist say, who entertained the generally-received opinions on the distribution of organic beings in accordance with our knowledge of the northern hemisphere (or, rather, in this imaginary case of both hemispheres), when he found these gravel beds abounding with Olivas, Volutns, and Terebras? — such 2 g 2 *