62 TIIE DOCTRINE OF DESCENT. 
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. 
. Carboniferous formation. 
Coal Measures. 
Millstone Grit. 
Mountain Limestone. 
9. Devonian formation. 
to. 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 Aluvium. 
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, although a portion of the organisms of which the 
remains occur in the Diluvial strata is extinct, much 
more still exists, these two formations are inseparably 
intermingled. 
To the Diluvium belong the vast mud deposits of 
the great rivers, alternating with sand banks, the clay 
and loess formations caused by the removal of the soil 
oo 
