I THE DARWINIAN HYPOTHESIS 9 
_ distinct from those that now live. Nor is this un- 
likeness without its rule and order. As a broad 
- fact, the further we go back in time the less the 
_ buried species are like existing forms ; and, the fur- 
ther apart the sets of extinct creatures are, the less 
‘they are like one another. In other words, there 
- has been a regular succession of living beings, each 
_ younger set, being in a very broad and general 
sense, somewhat more like those which now live. 
It was once supposed that this succession had 
been the result of vast successive catastrophes, 
destructions, and re-creations en masse; but 
catastrophes are now almost eliminated from 
geological, or at least paleeontological speculation ; 
and it is admitted, on all hands, that the seeming 
breaks in the chain of being are not absolute, but 
only relative to our imperfect knowledge; that 
species have replaced species, not in assemblages, 
but one by one; and that, if it were possible to 
have all the phenomena of the past presented to 
us, the convenient epochs and formations of the 
geologist, though having a certain distinctness, 
would fade into one another with limits as 
undefinable as those of the distinct and yet 
separable colours of the solar spectrum. 
Such is a brief summary of the main truths 
which have been established concerning species. 
Are these truths ultimate and irresolvable facts, 
or are their complexities and perplexities the 
mere expressions of a higher law ? 
