different arrangement of our seas and continents, destructive of the higher forms of life, and accompanied by the introduction of northern forms of partly corresponding classes.
Edward Forbes concluded from his researches in the AEgean that parallels in latitude are equivalent to regions in depth ; and he subsequently showed this hypothesis to hold good by the occurrence at various depths in southern seas of northern species of mollusca. Hence cold-water species of Testacea can have a much wider range in latitude than warm-water species. MM. D'Archiac and De Verneuil had already, on purely palaeontological grounds, concluded that those species which were found at many places, and in districts distant one from the other, are almost always those which have lived through many successive formations (systemes)* ; or, as it was better expressed by Mr. Rogers, " the species of which the geographical distribution is the widest have also the greatest vertical range." Reasoning from these data, M. D'Archiac observed that those geologists who saw " beds of different age everywhere where they found different fossils, were liable to make serious mistakes ; for the same bed taken at two distant points and having a natural difference of level, say of 300 feet, might present very distinct groups of species, and might lead to the erroneous conclusion that these two parts of the same bed were not contemporaneous "f. Edward Forbes also observed
- Bull. Soc. Geol. de France, vol. xiii. p. 260, 1842.
f Bull. Soc. Geol. de France, 2nd ser. vol. ii. p. 484, 1845. As the discussion which ensued on this communication bears on the subject of these deep-sea investigations, I give a few extracts from it, which may be new to some present : —
" M. de Verneuil ajoute que, sur les cotes de Suede et de Norvege, la ou la mer est assez profonde, M. le Professeur Loven, de Stockholm, a observe' parmi les mollusques une distribution verticale correspondant a leur distribution horizontale, suivant les latitudes. Ainsi, entre Gothenbourg et la Norvege, M. Loven a trouve a 80 toises de profondeur, des especes qui, sur la cote du Finmark, habitent a 20 toises ; plusieurs especes s'elevent meme sur cette derniere cote jusqu'a la region littorale, tandis que dans le sud, elles se tiennent toujours a, 12 ou 15 toises au-dessous du niveau de la mer."
" M. filie de Beaumont fait remarquer .... Aujourd'hui la temperature a la surface de la mer a l'equateur est de 27-1/2° [C], tandis qu'au fond elle est de 2°. II n'y a aucune raison de croire a ces differences autrefois." . ..." La tres-grande masse de la mer equatoriale est a une temperature tres-basse et seulement d'un petit nombre de degres au-dessus de zero."
M. Pouillet also, in his ' Elements de Physique,' vol. i. p. 166, 1847, speaking of deep-sea fishes, observes : " On peut juger par la que les regions delamer ont leurs peuples differents, non seulement suivant les climats, mais encore suivant les profondeurs."
vol. xxvii. e
