92 



Featherstonhaugh''s Geological Report. 



salt. Before these greater depths of the ocean had been 

 produced, its mean depth was more equally distributed over 

 the surface, and it is not difficult for us to understand how vast 

 beds of rock-salt might, under such circumstances, be formed, 

 by the evaporation of the waters of a high temperature. In 

 Europe the salt is usually found distributed above the coal 

 measures, but in the United States it is uniformly found lower 

 down. In both countries, however, the saline deposites 

 generally approach, and indicate a common origin, as if bodies 

 of salt w^ater had existed in such situations, perhaps in some 

 cases insulated, as to produce their evaporation. Superficial 

 incrustations of the same mineral are now found in various 

 parts of the west of Arkansas, caused by solar desiccation of 

 the natural salines. In the tertiary group, the fossils are 

 equally characteristic of the beds of the group in every part 

 of the world, receding in affinity from all previously examined 

 in proportion to their periods, but united by a common plan 

 and^ analogy. A slight acquaintance with the fossil shells 

 of the tertiary strata, will enable any individual to identify 

 the beds. Here the ammonites become extinct, and cones and 

 volutes begin to abound. Although it may be asserted that 

 the various fossiliferous strata contain characteristic organized 

 bodies by which strata can be identified, and of course which 

 separate them from other strata, yet it is not to be expected 

 that all the fossils of equivalent strata are identical in all 

 countries, although some of them are, as is the case with many 

 living species in both hemispheres. Whilst congeners in age 

 and in fact, their forms are influenced by physical laws, and 

 particular species are necessarily geographically limited by 

 climate and food. Where these are favorable, all the species 

 having a close affinity to each other may be found ;* and 



* Since calcareous matter is necessary to testaceous animals, we must infer that 

 a change in the mineral nature of their beds would be inconsistent with the pros 

 perous existence of any animals nnsuited to it : hence we find the greater number 

 ot fossil shells in Umestone beds, and in calcareous sandstones and shales ; very 



