Life Progressive. 407 



them. The great coal-fields of the Carboniferous Age, it is 

 now generally conceded, are the result of the growth in situ 

 of the plants which compose coal, as well as that they 

 grew on vast marshy or partially submerged tracts of level 

 alluvial land. 



While fossils enable us in many cases to arrive at impor- 

 tant conclusions as to the climate of the period in which they 

 lived, yet it is only in the case of marine fossils, which con- 

 stitute the majority of such remains, that we acquire such 

 knowledge, but it is mostly the temperature of the sea which 

 can thus be determined. However, let it be remembered 

 that, owing to the existence of heated currents, the marine 

 climate of a designated area does not necessarily imply a 

 correspondingly warm climate in the adjoining land, for 

 land-climates can only be determined by the relics of land- 

 animals or land-plants, and these are comparatively rare as 

 fossils. But all conclusions on this head are really based 

 upon the existing distribution of vegetable and animal life 

 upon the globe, and are therefore liable to be vitiated by the 

 considerations that no certainty exists that the' habits and 

 requirements of an extinct animal were exactly similar to 

 those of its nearest living relative ; that far back in time 

 groups of organisms, so unlike anything we know at the 

 present day, are met with, which render all conjectures of 

 climate based upon their supposed habits more or less uncer- 

 tain and unsafe ; that in the case of marine animals we are as 

 yet very far from knowing the precise limits of distribution 

 of many species within our present seas as to render con- 

 clusions drawn from living forms in relation to extinct 

 species unsatisfactory and, probably, incorrect ; and, finally, 

 that the distribution of animals to-day, is certainly depend- 

 ent on other conditions than climate alone, the causes limit- 

 ing the range of given animals being assuredly such as 

 belong to the existing order of things, and are different from 

 what they were in former times, not necessarily because the 

 climate has changed, but because of the alteration of other 



