Life Progressive. 407 
them. The great coal-fields of the Carboniferous Age, it is 
now generally conceded, are the result of the growth zw 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 
