CONTENTS. vii 



CHAPTER VIII. 



VOLCANIC ROCKS continued. 



Trap dikes sometimes project sometimes leave fissures vacant by decom- 

 position Branches and veins of trap Dikes more crystalline in the centre 

 (p. 105.) Foreign fragments of rock imbedded Strata altered at or near 

 the contact Obliteration of organic remains Conversion of chalk into 

 marble and of coal into coke (p. 108.) Inequality in the modifying influ- 

 ence of dikes Trap interposed between strata Columnar and globular 

 structure (p. 110.) Relation of trappean rocks to the products of active 

 volcanos (p. 114.) Submarine lava and ejected matter corresponds gene- 

 rally to ancient trap. 



CHAPTER IX. 



PLUTONIC ROCKS GRANITE. 



General aspect of granite Decomposing into spherical masses Rude colum- 

 nar structure Analogy and difference of volcanic and plutonic formations 



Minerals in granite, and their arrangement Graphic and porphyritic 

 granite (p. 121.) Occasional minerals Syenite Syenitic, talcose, and 

 schorly granites Eurite Passage of granite into trap Examples near 

 Christiania and in Aberdeenshire Analogy in composition of trachyte and 

 granite Granite veins in Glen Tilt, Cornwall, the Valorsine, and other 

 countries (p. 123.) Different composition of veins from main body of granite 



Metalliferous veins in strata near their junction with granite (p. 128.) 

 Apparent isolation of nodules of granite Quartz veins Whether plutonic 

 rocks are ever overlying Their exposure at the surface due to denudation 

 (p. 131.) 



CHAPTER X. 



METAMORPHIC ROCKS. 



General character of metamorphic rocks Gneiss Hornblende-schist Mica- 

 schist Clay-slate (p. 133.) Quartzite Chlorite-schist Metamorphic 

 limestone Alphabetical list and explanation of other rocks of this family 



Origin of the metamorphic strata (p. 135.) Their stratification is real 

 and distinct from cleavage On joints and slaty cleavage (p. 138.) Sup- 

 posed causes of these structures how far connected with crystalline action. 



CHAPTER XI. 



METAMORPHIC ROCKS continued. 



Strata near some intrusive masses of granite converted into rocks identical 

 with different members of the metamorphic series Arguments hence de- 

 rived as to the nature of plutonic action (p. 146.) Time may enable this 

 action to pervade denser masses From what kinds of sedimentary rock 

 each variety of the metamorphic class may be derived (p. 150.) Certain 

 objections to the metamorphic theory considered. 



