On the Geological Arrangement of Ancient Strata. 333 



mutest lands of the Pacific Ocean ; nay, even in the now frigid climates 

 of the Arctic and Antarctic circles. 



This uniformity of its inhabitants would seem to indicate a uniformity 

 of temperature, and other conditions of the primeval ocean, differing 

 from those which prevail in the present seas, and a difference in distri- 

 bution of animal life over the various regions of the earth. 



We shall not here enter into the changes which marine animals, and 

 ^especially testaceous molluscs, undergo, in consequence of differences 

 of locality, temperature, and other external circumstances, because this 

 is a subject which belongs more properly to considerations regarding the 

 past and present temperature of the general surface of the globe. It 

 may be remarked, however, that such external circumstances give rise 

 to changes, in many cases amounting even to specific differences, in the 

 appearance of the animals. Thus, the testaceous inhabitants of inland 

 ^eas and gulphs are pigmies compared to their congeners of the open 

 ocean ;* and not only size, but colour, and even form of shell, may be 

 changed. In those raised beaches which are so common in Scotland, 

 and on many of the coasts of the European continent, testacese are found 

 apparently with specific differences from those existing in the contigu- 

 ous seas. Thus, on tlie banks of the Clyde, species have been found 

 fiaving more of an arctic character than those of the same family at pre- 

 sent existing in that estuary, t Now, this may have arisen simply from 

 a change of level in the locality, altering, in some slight degree, the tem- 

 perature, such as a rise of the channel of the Frith, and a consequent 

 shallowing of the water. In this way, the depth of the waters of the 

 Clyde may have been formerly such as to permit of localities more ap- 

 proaching in temperature to that of the friths of arctic regions. 



If the above conclusions are found to be based on sound deductions, 

 our geological systems will, at least, require somewhat of revisal. 



In the first place, the mineralogical character of rocks will be that on 

 which their proper arrangement and classification must depend. Thus, 

 if calcareous mud, brought down by currents, is deposited at a certain 

 depth in the ocean, it becomes tenanted by producti and ganoid fishes. 

 The same mud, if deposited at a higher level, is taken possession of by 

 belemnites and ammonites ; in the one case, it is called carboniferous 

 limestone, in the other lias. 



The present nomenclature, too, of primary, secondary, and tertiary, 

 can, in many cases, only convey erroneous impressions. Tlie same may 

 t)e said of many other terms pointing out a precedency of formation or 

 relative age. 



Organic remains will henceforth indicate the respective, and, perhaps, 

 hy analogy with living species, the actual depth at which the strata in 

 which they arc contained were situated in the primeval ocean. They are 



* JG. Forbes, Esq. f •^ames Sqiith, £s^., Jordanhall, Edia. PhiL Journal. 



