The Harmony of Creation. 573 
ration by animals, we uniformly arrive at the same nega- 
tive results relatively to the supposition of progressive 
improvement of animal organisation. We must, therefore, 
accept it as proved, that no such progressive improvement 
has existed. Thirdly, no appreciable modification being 
found in the organs of respiration of animals from the most 
ancient epoch to the present,a great number of genera 
having always existed with the same characters since the 
first animalisation of the globe, it must be inferred that the 
vital elements have not changed, and that the media in 
which animals existed, whether air or water, have remained 
the same. Fourthly, the media of existence having been 
always the same, no change in these media can be adduced 
as a cause for the successive extinctions and reproductions 
of the fauna of the earth, which have been shown by geo- 
logical phenomena to have taken place during the succes- 
sive geological periods, a conclusion of immense importance 
in the history of the globe. Fifthly, all the researches 
which have been made in the fossil fauna, deposited in the ° 
strata of the earth, lead to a conclusion of high geological 
importance, that, until the epoch which immediately pre- 
ceded the appearance of the human race and the contem- 
poraneous tribes upon the globe, all that part of the earth 
which has undergone a close and accurate geological sur- 
vey, including France, England, Germany, Italy, Switzer- 
land, Spain, Portugal, part of Russia, and the adjacent seas, 
were inhabited by a fauna altogether tropical, and such as 
is at present found only under the torrid zone. We are 
forced, therefore, to the conclusion that, until the present 
period, the isothermal zones now observed had no existence. 
Of 1,473 fossil general genera hitherto discovered, sixteen 
only are found to exist in all the stages. The remaining 
1,457 are distributed in different proportions throughout 
the stages. In some cases it is seen that certain genera 
are only found ina single stage, in others they prevail in 
two stages, in others in three or more; but, save in rare 
and exceptional cases, when they prevail in two or more 
stages, these stages are in geological succession. This per- 
sistence of the genera is a very important geological and 
paleontological fact. The exceptions to it do not exceed 
3 per cent. of the entire number of fossil genera, and may, 
therefore, be regarded as arising from some accidental 
cause. ‘This peculiar distribution of generic forms of the 
fossils supplies to the geologist most useful stratigraphical 
tests. Thus, if a genus known to exist only in one pecu- 
