302 On the Palceontologp of South Ameriea. 



In fig. 2, the piston is at half-stroke, ascending, ^rid the 

 position of the valve is reversed from that in fig. 1. 

 Fig. 3 is a front view and section of the valve. 



John Maxton. 



LfiitH ENGiNE-WORKS, 24<A Jamuzry l?i43. 



General Oomiderations regarding the Paleontology of South 

 America compared with that of Europe. By M. Alcide 

 D'Orbigny.* 



At the period when the gneiss system of rocks was being 

 deposited beneath the hot oceans which must then have co- 

 vered the globe, animal existence could not have been main- 

 tained ; and accordingly, in these beds, no trace of any ani- 

 mals has ever been detected. We may even go further, and 

 affirm that the earlier deposits of the Silurian system were 

 still devoid of them, at least in the American seas. And, in 

 fact, three-fourths of the predominating phylladian rocks, re- 

 presenting the Silurian in the New World, are destitute of or- 

 ganic remains — the earliest having appeared only towards the 

 termination of that period. At that epoch, the Silurian ocean 

 presented, in the southern hemisphere, an immense surface, 

 whereupon there existed, as in Europe, different species of Lin- 

 gular Orthis, Calymene^ and Asaphus^ resembling in form those 

 of the Old World, and identical with them. The uniform dis- 

 tribution of the species of this formation over all latitudes, 

 from the torrid zone to the frozen regions of Russia, denotes a 

 heat over the surface of the globe, so strong, that it extin- 

 guished the difference of temperature which is now referable to 

 the difference of latitude. 



Causes undoubtedly effecting new dislocations of the earth's 

 crust, annihilated all the animals of the Silurian system ; and 

 the strata which overwhelmed them were themselves covered 

 with new deposits. To the muddy sands of the American Si- 

 lurian strata, quartz sands succeeded. A distinct fauna arose 



* These Considerations are extracted from the Paleontological portion, not 

 yet published; of M. D'Orbigny *s Voyage dans VAvwrique miridionale. 



