62 THE DOCTRINE OF DESCENT. 



Middle Brown Jura (Dogger). 

 Lower Black Jura (Lias). 



6. Triassic formation or New Red Sandstone. 



Keuper or Variegated Marls. 



Muschelkalk. 



Variegated Sandstone. 



7. Permian formation or Dyas. 



Zechstein (Magnesian Limestone or Dolomitic Conglomerate) 

 Rothliegendes or Red Conglomerate. 



8. Carboniferous formation. 



Coal Measures. 

 Millstone Grit. 

 Mountain Limestone. 



9. Devonian formation. 



10. Silurian formation. 



11. Cambrian formation. 



12. Laurentian formation. 



Although we are not writing on geology, a short 

 explanation of these strata will be requisite, as their 

 mutual relations also throw light on the nature and 

 distribution of the contemporaneous organisms. All 

 displacements of earth which we now see occurring by 

 means of rain, rivers, sea and other natural forces 

 which have taken place in historic times, in short, in 

 the so-called Present, such as the great delta deposits, 

 and the moraine formations of our glaciers, are ascribed 

 to the Alluvium. 



It was formerly supposed that its limits might be dis- 

 tinguished from the Diluvium by the appearance of man, 

 but as it is now, and always has been impossible to 

 affirm anything positive respecting that epoch, and as, al- 

 though a portion of the organisms of which the remains 

 occur in the Diluvial strata is extinct, much more still ex- 

 ists, these two formations are inseparably intermingled. 



To the Diluvium belong the vast mud deposits of 



