22 AGRONOMY 



and quartzites are good illustrations of metamorphic rocks. 

 By consulting the following table the student should have 

 no difficulty in discovering to which group the rocks in 

 his own region belong. 



TABLE OF ROCKS 

 I. IGNEOUS. 



1. Granite. 



2. Basalt. 



3. Diorite. 



4. Lava. 



II. SEDIMENTARY, 01: A^rF.ors. 



A. Inorganic. 



1. Argillaceous shale (formed from clay). 



2. Silicious. 



a. Sandstone (formed from sand). 



I. Conglomerate (formed from pebbles). 



c. Breccias (formed from irregular fragments). 



3. Chemical bog iron, rock salt, gypsum. 

 R. Organic. 



1. Calcareous limestone (formed from animal remains). 



2. Carbonaceous soft coals (formed from plants). 



3. Silicious diatom earth, chert. 



III. METAMORPHIC. 



1. Slate (derived from shale). 



2. Quartzite (derived from sandstone). 



3. Marble (derived from limestone). 



4. Anthracite (derived from soft coals). 



Changes in mantle rock. The weathered fragments of the 

 bed rock have not lain undisturbed where they fell. The 

 work of weathering is unceasing. Little by little the parti- 

 cles have been reduced in size ; running water has sorted 

 them over time and again ; floods from the melting ice sheet 

 have spread them out; ants, earthworms, and other animals 

 have slowly turned them over, bringing deeper layers to the 



