DISTRIBUTION. 41 



Subjoined is a table giving the more important subdivisions 

 of the three great geological periods, commencing with the 

 oldest rocks and ascending to the present day. 



I. PALAEOZOIC OR PRIMARY ROCKS. 



1. Laurentian. (Lower and Upper.) 



2. Cambrian. (Lower and Upper, with Huronian Rocks?) 



3. Silurian. (Lower and Upper.) 



4. Devonian, or Old Red Sandstone. (Lower, Middle, and 

 Upper.) 



5. Carboniferous. (Mountain-limestone, Millstone Grit, and 

 Coal-measures.) 



6. Permian. (=the lower portion of the New Red Sand- 

 stone.) 



II. MESOZOIC OR SECONDARY ROCKS. 



7. Triassic Rocks. (Bunter Sandstein, or Lower Trias ; 

 Muschelkalk, or Middle Trias ; Keuper, or Upper Trias). 



8. Jurassic Rocks. (Lias, Inferior Oolite, Great Oolite, 

 Oxford Clay, Coral Rag, Kimmeridge Clay, Portland Stone, 

 Purbeck beds.) 



9. Cretaceous Rocks (Wealden, Lower Green sand, Gault, 

 Upper Greensand, White Chalk, Maestricht beds.) 



III. KAINOZOIC OR TERTIARY ROCKS. 



TO. Eocene. (Lower, Middle, and Upper.) 



IT. Miocene. (Lower and Upper.) 



12. Pliocene. (Older Pliocene and Newer Pliocene.) 



13. Post-tertiary. (Post-pliocene and Recent.) 



