On the Geological Arrangement of Ancient Strata. 329 



It seems to be now also established, that marine animals take up their 

 localities at depths, varying according to their classes and genera, and 

 even their species. Every one who has dredged for mollusks must have 

 remarked that particular species are only to be found in particular loca- 

 lities, and Professor E. Forbes, in a paper read before the last meeting 

 of the British Association, has shewn, from his researches in the -^Egean 

 Sea, that there are about eight regions in that inland gulph, varying 

 from a depth of 2 to 230 fathoms, tenanted by its particular groups of 

 mollusca and radiata. These zones or regions are, in many respects, 

 Mr Forbes remarks, equivalent to parallels of latitude in regard to the 

 distribution of species. 



There is every reason to believe, that fishes also observe a similar ar- 

 rangement with regard to their localities ; for, in a general way, these 

 inhabitants of the ocean have for a long time been divided into littoral 

 and pelasgic, as well as the testaceous molluscs. 



We know, indeed, that many families of fishes are strictly confined 

 to particular localities. Some inhabit the deep seas, as the cod and had- 

 dock ; some the flat shallow sands, as the rays and other flat fish ; while 

 numerous species are confined to the shallow shores of bays and es- 

 tuaries. On the whole, then, we shall have, perhaps, a not inaccurate 

 idea of the condition of the ocean, if we compare a descending section 

 of it to a tropical mountain, which we find divided into zones of tempe- 

 rature, each zone being characterized by distinct groups of plants and 

 animals. 



Now, such an arrangement in our existing seas appears to us to fur- 

 nish a very simple and adequate explanation of the condition of our 

 ancient geological strata. For when we find a series of such strata con- 

 taining distinct beds of fossiliferous remains, grouped in regular and 

 successive order, we at once perceive that they are thus arranged ac- 

 cording to the localities which the living organisms maintained in 

 their contemporaneous ocean, and that this localization is entirely due to 

 the respective depths of water in which each species of animal was ac- 

 customed and adapted to live. 



On this view of the subject, we can readily explain why the upper 

 series of strata are so full of organic life, — why, as we descend, that or- 

 ganic beings become more and more rare, till at last we arrive at a line 

 where all traces of plants and animals cease. 



Suppose that in the present day some great eruption of plutonic rocks 

 were to elevate a portion of our seas — the basin of the Forth, for instance* 

 extending in a line outwards into the deep sea, we should then have in 

 the upheaved strata an illustration of the successive localization of its 

 marine inhabitants. In what would be called the upper or newer strata, 

 we should find fluviatile fishes and mollusks imbedded in calcareous 

 mud or shale ; to these would succeed beds swarming with marine 

 testacea ; farther on, amidst the sandstone debris and conglomerate, the 

 various species of rays and other flat fishes would present themselves j 



VOL. XXXVI. NO. LXXII. APRIL 1844. Y 



