62 GEOLOGY. 



Potamol'ogy (Gr. pofamos, a river, and logos, a discourse). — 



A treatise on rivers. 

 Zone. — A division of the earth with respect to the temperature 



of different latitudes. 



GEOLOGY. 



Geol'ogy (Gr. (/e, the earth, and logos, a discourse). — The sci- 

 ence which treats of the structure and mineral constitu- 

 tion of the glohc and tlie causes of its physical features. 



Lithol'ogy, or Petrology ( Gr. Uthos or petros, a stone, and 

 logos, a discourse). — That division of geology which treats 

 of rocks in their mineralogical aspect. 



Stromatorogy (Gr. stroma, a bed, and logos, a discourse). — 

 Tliat division of geology which considers the stratified 

 rocks in their clironological order, as exhibiting different 

 phases of the history and development of the globe itself, 

 and in their fossil contents setting forth the progress of 

 life upon its surface. 



GKAND DIVISIONS OF GEOLOGICAL TIME. 



1. Azo'ic. — The preparatory time for the commencement of 

 the systems of life. 



2. Paleozo'ic. — Including (1) The Age of Mollusks, or Silu- 

 rian ; (2) The Age of Fishes, or Devonian ; (3) The Age 

 of Coal Plants, or Carboniferous. 



3. Mesozo'ic. — Including the Eeptilian Age. 



4. Cenozo'ic. — Including the IMammalian Age. 



5. The Age of Mind, or the Human Era. 



E'ocene (early dawn). — A term applied to the earlier tertiary 



deposits, in which are a few organic remains of existing 



species of animals. 

 Mi'ocene (less recent). — The middle division of the tertiary 



strata, containing fewer fossil shells of recent species than 



the pliocene, but more than the eocene. 

 Pleis'tocene (most recent). — The newest of the tertiary strata, 



which contains the largest proportion of living species of 



shells. 

 Pli'ocene (more recent). — A name given to the most modern 



tertiary deposit, in which most of the fossil shells are of 



recent species. 



