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deposits were laid down ; but these conditions are probably 
rarely carried out. This is unquestionably true, if we only 
knew how thick the formation would need to be. This we do 
not know, and therefore it will always be open for each observer 
to hold his own opinion on this point. Some will be of opinion 
that the uninterrupted deposition of fifty or a hundred feet of 
sediment would amply fulfil the above conditions. Mr. Darwin, 
on the other hand, believes that a whole formation would not 
be sufficient for this purpose; and there does not appear at 
present to be any means of coming to an agreement on this 
point. 
d. That every formation has been more or less intermittent 
in its accumulation is unquestionably true, since the dividing- 
line between every stratum and the next undeniably marks a 
pause in the work of deposition. We have, however, no proof 
that these pauses have been always of even approximately the 
same length. Sometimes we have reason to believe that they 
have been very long; at other times there are grounds for 
thinking that they were comparatively very short. We can, 
therefore, come to no positive conclusion, as to the amount of 
time represented in this way, and can thus attach no definite 
value to any argument derived from this source. 
e. The last of Mr. Darwin’s arguments which I may notice 
is that we have no right to look in our geological formations 
for “ an infinite number of those fine transitional forms, which, 
on our theory, have connected all the past and present species 
of the same group into one long and branching chain of life.” 
On the contrary, we have only a right to look for a few of 
these transitional links, and such are actually found to exist in 
nature. To this it may be replied that whilst we have assuredly 
no right to ask for an infinite series of links, we have a right 
to ask for a much more perfect series of links than has as yet 
been brought to light. The transitional forms which are at 
present known to us, — and there are more of them than might 
be imagined, — might be sufficient to give an apriori probability 
to some theory of evolution ; but they can hardly be said to be 
in any single instance sufficient to be accepted as proof of the 
special explanation of evolution advocated by Mr. Darwin. 
(5. On the Succession of Life in a Series of Conformable De- 
posits. — We have seen that Mr. Darwin admits that the absence 
of a series of graduated intermediate forms betw r een the species 
at the commencement of any single formation and those which 
lived at its close, is a great stumbling-block in the way of his 
theory. Let us now see what we actually do find in such a 
case, having in the meanwhile regard w'holly to the facts, and 
