324 
GEOLOGICAL SUCCESSION, 
Chap. X. 
don and Horse, it miglit at least have been inferred that 
they had lived during one of the later tertiary stages. 
When the marine forms of life are spoken of as 
having changed simultaneously throughout the world, 
it must not be supposed that this expression relates to 
the same thousandth or hundred-thousandth year, or 
even that it has a very strict geological sense; for if 
all the marine animals which live at the present day in 
Europe, and all those that lived in Europe during the 
pleistocene period (an enormously remote period as 
measured by years, including the whole glacial epoch), 
were to be compared with those now living in South 
America or in Australia, the most skilful naturalist 
would hardly be able to say whether the existing or the 
pleistocene inhabitants of Europe resembled most closely 
those of the southern hemisphere. So, again, several 
highly competent observers believe that the existing 
productions of the United States are more closely related 
to those which lived in Europe during certain later ter¬ 
tiary stages, than to those which now live here; and 
if this be so, it is evident that fossiliferous beds de¬ 
posited at the present day on the shores of North 
America would hereafter be liable to be classed with 
somewhat older European beds. Nevertheless, looking 
to a remotely future epoch, there can, I think, be little 
doubt that all the more modern marine formations, 
namely, the upper pliocene, the pleistocene and strictly 
modern beds, of Europe, North and South America, and 
Australia, from containing fossil remains in some degree 
allied, and from not including those forms which are 
only found in the older underlying deposits, would be 
correctly ranked as simultaneous in a geological sense. 
The fact of the forms of life changing simultaneously, 
in the above large sense, at distant parts of the world, 
has greatly struck those admirable observers, MM. 
