14 THE PROSPECTORS HANDBOOK. 



Sand (in which the grains are loose). 



Clay (silicate of alumina and of a plastic nature). Slates (hardened 



clay, which displays cleavage across the bedding). 

 Shales (hardened laminated elay). 

 Marl (clay containing carbonate of lime) . 

 Loam (clay mixed with fine sand). 

 Flint (nearly pure silica). 



Limestone, chalk, marble, &c. (made up of carbonate of lime). 

 Delomite (carbonate of lime and magnesia) . 



In addition to these may be mentioned volcanic ash, deposits from 

 hot springs, &c. 



With regard to the age of granite, which formerly used to 

 be considered the oldest rock, and also that of the meta- 

 morphic rocks, the latter are of various ages, and really 



Great 



ft 7 - 6 54 3 2A 2 4 



FIG. 5. GENERAL SECTION FROM THE SIERRA NEVADA INTO CALIFORNIA. 



1, Granitic and gneissic rocks. 2, Slates and sandstone. 2A, Crystalline and 

 irietamorphic rocks, slates, gnejss, and gneissic rocks, in some places quartzite 

 (gold-bearing). 3, Devonian and carboniferous limestones, with shales and 

 sandstones (gold and silver bearing). 4, Coal measures. 5, Triassic rocks. 

 6, Oolitic. 7, Liassic. 8, Tertiary. 



represent certain rocks metamorphosed. It is supposed, 

 from its nature, that granite could not have been subjected 

 to a very great heat (although I have classed it as igneous), 

 and though, while evidence does not deny that the basis of 

 rock formations may be granite, still it shows that the intru- 

 sive granitic rocks which are met with in the crust of the 

 earth belong to various ages; and it may be taken for 

 granted that the formation of granite in another geological 

 formation is newer than the rock which it penetrates and 

 older than the strata deposited on it. 



Not only are rocks deposited by the agency of water in 



