LIFE AND OKGANISATION. 93 



give evidence to the same fact of local limitation ; and even 

 lake and river fishes demonstrate it, comparatively narrow 

 though the spaces are which they occupy. We may seem to 

 see reason why the Salmon, found in all countries bordering 

 round the Arctic Circle, should nowhere exist in the Southern 

 hemisphere. But how are we to explain the different families 

 of fish, found by Agassiz in each of the great fresh-water 

 lakes of North America, connected as they are by a common 

 river ? Or how the fishes peculiar to the Ohio and many other 

 rivers ? Or the species limited in existence to some of our 

 own rivers and lakes ? 



Such instances, which might be endlessly multiplied, show 

 how curious are the problems belonging to this part of natural 

 history ; and how perplexed in every part by the doubt of 

 what may belong to a primitive geographical distribution of 

 created beings ; what to the revolutions of the surface of 

 the globe, paroxysmal or gradual, which have since inter- 

 vened. The argument for the former, supported as it is by 

 the complete analogy of vegetable life, is too strong not to 

 compel belief; though leaving it doubtful to what extent the 

 limitations of localities and species originally existed. Fur- 

 ther research may do something towards clearing away these 

 doubts, but can never wholly remove them. The unques- 

 tionable changes in climate and other physical conditions 

 essential to life, from geological revolutions on the earth's 

 surface ; and the mighty influence of Man when he became 

 a tenant of the globe, in multiplying, destroying, or trans- 

 planting whatever of the living creation existed around him, 

 have removed many of the marks or outlines which might 

 have denoted this primitive distribution. Fossil geology to a 

 certain extent comes in aid of the research ; though in solving 

 some questions it evokes others not less difficult. In the 

 vast periods of time through which it carries us, we see the 

 same revolutions of surface, elevations, depressions, and 



