CONTENTS. xm 



PAGE 



leading minerals of igneous rocks, 399. The feldspathic 

 minerals, 400. The ferromagnesian minerals, 400. Summary 

 of salient facts, 401. 



The Nature of Molten Magmas 401 



Time required in crystallization, 402. Successive stages 

 of crystallization, 403. 



The Fragmental Products of Sudden Cooling 404 



Pyroclastic rocks, 404. 



The Glassy Rocks 406 



The solid glasses, 406. The first stages of crv^stalli ation, 

 407. The obsidians, 407. 



Special Structures 410 



Flow structure, 410. Amygdaloids, 411. 



The Porphyrttic Rocks 411 



The Phanerocrystalline Rocks 412 



The phanerites, 412. The granites, 413. The syenites, 

 415. The d orites, 416. The gabbros, 416. The perido- 

 tites, 416. The basalts, 417. The dolerites, 417. General 

 names, 418. 



Derivation .of Secondary Rocks 420 



Regolith, 422. Disrupted products: arkose and wacke, 

 422. Disintegrated products, 422. 



Classes of Sedimentary Rocks 422 



Shales, sandstones, and conglomerates, 422. Limestones 

 and dolomites, 424. Precipitates, 424. Iron-ore beds, 425. 

 Silicious deposits, 425. Organic rocks, 426. 



Internal Alterations of Rocks 426 



Oxidation and deoxidation, 427. Solution and deposi- 

 tion, 427. Hydration and dehydration, 428. Carbonation 

 and decarboriation, 429. Molecular rearrangements, 431. 



The Salient Features of Rock Descent 431 



The Reascensional Process 432^ 



Induration under ordinary pressures and temperatures, :t ' 

 432. Cavity filling, 436. Fissure filling; veins, 437. Solu- 

 tion as v/ell as deposition, 437. Concretions, 438. Replace- 

 ments and pseudomorphs, 439. Incipient crystallization, 

 439. 



Reconstruction under Exceptional Conditions 440 



Slaty structure, 441. Foliation, schistosity, 443. Meta- 

 morphism by heat, 446. Metamorphism by heat and lateral 



