272 L. Agassiz on the Diversity 
but also of the local fauna of each period. Agassiz states 
that our present list of fossils teem with chronological errors 
of the worst kind, arising from false identifications of strata. 
This we can well imagine, because our mineralogical, (geo- 
logically speaking) stratigraphical, and petralogical know- 
ledge are extremely vague. Agassiz further shows in this 
paper that the number of false identifications of organic re- 
mains that have accumulated in zoological works are truly 
frightful ; and he maintains that the materials thus accumu- 
lated are no longer fit to be used in the discussion of the 
questions that have been raised with the modern professors 
of geology, and that a thorough revision of all the identifi- 
cations of species is required,—and shows that without a 
complete knowledge of species, it is a hopeless task to at- 
tempt to determine the order of succession of the fossils in 
different geological formations. 
He concludes this valuable paper with important remarks 
on the disputed question of the period of appearance of dico- 
tyledonous plants in the geological science. He maintains 
that the dicotyledonee are inferior to the monocotyledonez, 
and that there exists a similar gradation of types in the 
vegetable as in the animal kingdoms. 
There is a view generally entertained by naturalists and 
geologists that genera and species of animals and plants are 
greatly more numerous at the present age of the world than 
in any previous geological period. This seems to me an entire 
misconception of the character and diversity of the fossils 
which have been discovered in the different geological forma- 
tions, and to rest upon estimates which are not made within 
the same limits, and with the same standard. Whenever a 
comparison of the diversity and number of fossils of any geo- 
logical period has been made with those of the living animals 
and plants belonging to the same classes and families, it has 
been done under the tacit assumption which seems to me 
entirely unjustifiable, that the fossils formerly inhabiting our 
globe are known to the same extent as the animals which 
live at present upon its surface ; while it should be well 
understood that however accurate our knowledge of fossils - 
: pat a, ed = . 
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