RESOURCES 80
ECONOMIC FEATURES OF THE COMMON ROCKS 80
Granite 82
Basalt and related types 82
Limestone, marl, chalk 82
Marble 83
Sand, sandstone, quartzite (and quartz) 84
"Sand and gravel" 84
Clay, shale, slate 85
The feldspars 86
Hydraulic cement (including Portland, natural, and
Puzzolan cements) 86
GEOLOGIC FEATURES OF THE COMMON ROCKS 88
Building stone 88
Crushed stone 90
Stone for metallurgical purposes 91
Clay 91
Limitations of geologic field in commercial investigation
of common rocks 92
SOILS AS A MINERAL RESOURCE 94
Origin of soils 94
Composition of soils and plant growth 96
Use of geology in soil study 97