Paleontology. 159 
leaving an impression; that this surface should 
afterwards have hardened sufficiently to retain the 
impression ; that it should then have been protected 
from the erosion of water, as well as from the dis- 
integrating influence of the air ; and yet that it should 
not have sunk far enough beneath the surface to have 
come within the no less disintegrating influence of 
subterranean heat. Remembering thus, as a general 
rule, how many conditions require to have met before 
a fossil can have been both formed and preserved, 
we must conclude that the geological record is pro- 
bably as imperfect in itself as are our opportunities of 
reading even the little that has been recorded. If we 
speak of it as a history of the succession of life upon 
the planet, we must allow, on the one hand, that it is 
a history which merits the name of a “chapter of 
accidents”; and, on the other hand, that during the 
whole course of its compilation pages were being 
destroyed as fast as others were being formed, while 
even of those that remain it is only a word, a line, or 
at most a short paragraph here and there, that we are 
permitted to see. With so fragmentary a record as 
this to study, I do not think it is too much to say 
that no conclusions can be fairly based upon it, 
merely from the absence of testimony. Only if the 
testimony were positively opposed to the theory of 
descent, could any argument be fairly raised against 
that theory on the grounds of this testimony. In 
other words, if any of the fossils hitherto discovered 
prove the order of succession to have been incom- 
patible with the theory of genetic descent, then the 
record may fairly be adduced in argument, because 
we should then be in possession of definite information 
