28 



OUTLINES OF GEOLOGY. 



latter may be called ancient. Intermediate between these 

 we find the evidence of one or more great catastrophes, by 

 which the whole surface of the present land was exposed to 

 the action of water, and actually submerged. The deposits 

 from those floods we shall rank with modern formations, un- 

 der the term of diluvial. 



60. Modern formations may be distinguished into four 

 orders : — 



1. Alluvial; 



2. Chemical; 



3. Diluvial; 



4. Volcanic. 



61. Ancient formations may be either stratified or not. 

 The ancient stratified formations may be divided into five 



orders : — 



1. Superior; 



2. Supermedial; 



3. Medial; 



4. Submedial; 



5. Inferior. 



Ancient rocks, not stratified, are arranged in six orders:— 



1. Granitoid ; 



2. Porphyritic ; 



3. Ophiolitic ; 



4. Trachytic; 



5. Trapp; 



6. Volcanic. 



I; MODERN FORMATIONS. 



ORDER I. ALLUVIAL. 



62. Alluvial formations may be either of animal or vege- 

 table origin, or of one wholly mechanical. 



