182 



REPORT — 1856. 



markable. All the American palaeozoic formations appear to contain fewer species 

 in common than do the European ; and even strictly sequent formations divided by 

 no crisp physical plane, display decidedly abrupt transitions in their organic types. 

 No doubt every such sharp palaontological horizon coincides with a horizon of true 

 physical discontinuity, or sudden change at least, somewhere within the same 

 basin. Indeed, such palajontological planes may be accepted as evidence of im- 

 portant revolutions in the level of the ancient oceanic floor. This horizon of the 

 upper limit of the Matinal rocks is incontestably the sharpest paleeontologically 

 within the whole palaeozoic system of the Appalachian basin, whether we measure 

 it by the smallness in the proportion of the species which bridge the gulf, or by the 



Palceontological relations of the American and European Palceosoic Strata. 



Coal. 



Carb. Limest. 



Old Red Sandstone. 



