64 M. Alcide d'Orbigny on Living and Fossil Molluscs. 



other on the surface of our planet. When we fail to find, 

 at points in the vicinity of the place where their distinct 

 faunas at present appear, a sufficient explanation of the cir- 

 cumstance from chains of mountains, we must seek it more 

 remotely, in points still unknown to science, or suppose that 

 if these terrestrial systems are the cause, many of them have 

 been destroj-ed by new sinkings. Chains of mountains, more- 

 over, are only the visible portion of the dislocation of the 

 globe, while the sunk portion, perhaps more considerable, 

 being for the most part covered, is unknown to us, and will 

 always continue to be so. 



" In a word, the separation of stages and formations by 

 distinct faunas, is nothing more than the visible consequence 

 of the varied elevations and sinkings of the earth's crust in 

 all its parts. 



" I may further remark, from the uniform distribution of 

 the same beings, that, up to the period of the cretaceous for- 

 mations,* the internal heat of the earth has destroyed the 

 whole influence of latitude and polar cold. If exterior at- 

 mospheric influence on the distribution of beings on the earth's 

 surface did not then exist, all the faunas anterior to the ci'e- 

 taceous formations certainly owe their limitation by forma- 

 tions to the great dislocations of the globe. It would be at 

 a posterior date that the influences of latitude rendered the 

 division into basins more complicated, multiplied the local 

 faunas, as is seen in the tertiary formations, and destroyed 

 that uniformity of distribution which is observed in the most 

 ancient formations. 



" Assuming as a basis, the superposition and points of 



separation more or less decided among the faunas which have 



succeeded each other, from the first appearance of animals on 



the globe up to the present time, the following, in the order 



of their succession, are the formations and stages deduced 



from geological and palaeontological observations. 



Pal-eozoic Formation. 

 First, Silurian stage. 

 Second, Devonian stage. 

 Third, Carboniferous stage. 

 Fourth, Permian stage. 

 Fifth, Triasic stage. 



* See my particular woi'k on Coquilles Foisiles de Colombie. 



