CHRONOLOGICAL SUCCESSION OF STRATIFIED ROCKS. 41 



or Palceozoic rocks (Gr. palaios, ancient ; zoe, life), because of the 

 wide divergence of their animals and plants from any now existing 

 upon the globe. The Triassic, Jurassic, and Cretaceous systems are 

 grouped together as the Secondary or Mesozoic formations (Gr. mesos, 

 intermediate ; zoe, life), because their organic remains are interme- 

 diate between those of the Palaeozoic period, and those of more 

 modern strata. The Eocene, Miocene, Pliocene, and Pleistocene 

 rocks are grouped together under the head of Tertiary or Kainozoic 

 rocks (Gr. kainos, new ; zoe, life), because the fossil animals and 

 plants which they contain approximate in character to those now 

 existing upon the globe. 



According to the recommendations of the International Geological 

 Congress, the following names should be employed for the larger and 

 smaller divisions of the stratified rocks and the time-divisions to which 

 these correspond, the terms being arranged in order of their compre- 

 hensiveness. 



Divisions of sedimejitary Corresponding chrono- 



formatio?is (" terranes "). logical terms. 



Group. Era. 



System. Period. 



Series (or Section). Epoch. 



Stage (or Beds). Age. 



The term " formation," very commonly employed by British geologists, 

 is perhaps best retained as a loose general term to indicate any set of 

 beds, large or small, which have some common characteristic, either as 

 to mineral nature or fossil contents, or as to the mode in which the de- 

 posit has been formed. If used in a defi?iite sense, it should be employed 

 with reference to the mode of formation or the lithological nature of the 

 rocks ; so that we may suitably speak of the " Chalk Formation," or 

 the " Coal Formation," or of a " marine formation," or a " lacustrine 

 formation." 



The following table exhibits the great geological " systems," as 

 developed in Europe, in chronological order, beginning with the 

 youngest, the more important and typical British representatives of 

 each being likewise mentioned : — 



General Classification of Post-Arcilean Fossiliferous 

 Deposits. 



£ fi. Recent Formations. — Deposits now in process of formation 



W . J in seas, rivers, and lakes, and on land, such as the sands and 



5-1 ^ I muds of shallow seas, modern calcareous deposits like shell- 



o§ 1 beds, coral-reefs, &c, deep-sea muds, shell -marls, river- 



o '3 J gravels, peat-mosses, &c. 



o> i 2 - Quaternary or Pleistocene Formations. — Post-glacial, 



g ^ 1 Glacial, and Pre-glacial deposits, in which the Molluscs be- 



£ ^ I long to existing species, but some of the Mammals are refer- 



< H I able to extinct forms. Often grouped with the preceding 



W \ under the general name of the " Post-tertiary deposits." 



