196 Proceedings of the Royal Physical Society. 



of the British systems. To abide by these systems were to 

 set up our petty archipelago as the type of the wider world, 

 and. to retard the progress of geology ; and. we may rely on 

 it that the time is fast drawing near when we must both 

 modify and intercalate — modify what we now consider sys- 

 tems, and intercalate others to which there is no equivalent 

 in these islands. It is true that, under the present " syste- 

 mal arrangements," geology has made most excellent pro- 

 gress, and these on that account should not be lightly aban- 

 doned ; but to be ever forcing unnatural co-ordinations is 

 obstructive alike to truth and the labours of the distant 

 observer. As the old arrangements of Lehman and Werner 

 gave way to the wider knowledge of the present day, so 

 we may naturally expect the arrangements of the present 

 to be superseded by the more exact information of future 

 observers. 



Contemporaneity. — And this difficulty of co-ordination 

 brings us, in the fifth place, to remark on the very difficult 

 but most important question of contemporaneity, or contem- 

 poraneous formations. Hitherto the general idea has been 

 that identity of genera and species in any set of strata, 

 however widely separated, was proof of contemporaneity of 

 deposit. Founding on this notion, a thousand facts in geo- 

 logy became inexplicable ; but believing that species and 

 genera in time past had their centres and areas of distribu- 

 tion just as they have at the present day, and that under 

 the oscillations of sea and land they may have taken ages 

 to travel from one hemisphere to another, the difficulties 

 vanish, and we require to call in no abnormal conditions of 

 universal sameness of life, sameness of climate, changes 

 in the earth's axis of rotation, or such like causes, at total 

 variance with all that we know of the present ordainings 

 of the universe. Identity of species, therefore, unless in 

 limited areas, instead of proving contemporaneity of de- 

 posit, would go to prove the reverse, and would merely 

 show that the areas in which they are now found fossil 

 had at one time or other the means of transference placed 

 between them. From this view, then, it by no means fol- 

 lows that the palaeozoic coal-fields of America were contem- 



