CONTENTS. 



xi 



CHAPTER XXIV. 



ON THE DIFFERENT AGES OF THE PLUTONIC ROCKS. 



Difficulty in ascertaining the precise age of a plutonic rock — Test of age by 

 relative position — Test by intrusion and alteration — Test by mineral compo- 

 sition — Test by included fragments — Recent and Pliocene plutonic rocks, 

 why invisible (p. 283.) — Tertiary plutonic rocks in the Andes — Granite 

 altering cretaceous rocks (p. 286.) — Granite altering Lias in the Alps and in 

 Sky — Granite of Dartmoor altering Carboniferous strata — Granite of the Old 

 Red sandstone period — Syenite altering Silurian strata in Norway (p. 289.) — 

 Blending of the same with gneiss — Most ancient plutonic rocks — Granite 

 protruded in a solid form (p. 291 .) — On the probable age of the granite of 

 Arran in Scotland. 



CHAPTER XXV. 



ON THE DIFFERENT AGES OF THE METAMORPHIC ROCKS. 



Age of each set of metamorphic strata twofold (p. 294.) — Test of age by fossils 

 and mineral character not available — Test by superposition ambiguous — 

 Conversion of dense masses of fbssiliferous strata into metamorphic rocks — 

 Limestone and shale of Carrara — Metamorphic strata of modern periods in 

 the Alps of Switzerland and Savoy (p. 296.) — Why the visible crystalline 

 strata are none of them very modern — Order of succession in metamorphic 

 rocks (p. 299.) — Uniformity of mineral character — Why the metamorphic 

 strata are less calcareous than the fossiliferous (p. 301.) 



