CONTENTS. vii 



districts of Crystalline Rocks, 22. Application of current views in Anioricun 

 (Jeological Literature, 23. A.ssociation of Eruptive and Volcanic Rocks, 2.'J. 

 Origin of Crystalline Rocks, 2.3. Application of current views to Vesuvius in 

 the time of Strauo, 24. Principles to bo employed in studying regions of 

 Crystalline Rocks, 24. Materials of the earliest formed Lands of eruptive origin, 

 24. Application of the term Eruptive or Volcanic in this work, 24. The younger 

 Volcanic and the older Plutonic Rocks form a continuous series, 24. 



SECTION in. 



The Origin and Relations of the jNIineral Constituents of Hocks . . . 2.^30 



The constituents of rocks fall into three classes, 25. Two divisions of the first 

 class, 25 ; action of the Magma on Minerals of the first division, 25. Liclusions 

 in eruptive rocks, 25, 26. Action of Lava on Inclusions, 26. Microscopic charac- 

 ters of Eruptive Rocks opposed to the theory of their derivation from Sediments, 

 26. Mineral products of the crystallization of a magma, 26. Mineral products 

 of rock alteration, 26. The chemical constitution of altered rocks not es-sentially 

 changed, 26. Cause of rock alteration, 27. Alteration a character of the rock 

 mass as a whole, 27. Altered eruptive rocks tend to simulate the features of 

 sedimentary forms, 27. The general tendency of rock alteration, 27, 28. The 

 concentration of ores in rocks and veins attendant upon rock alteration, 28. Ores 

 of mechanical and eruptive origin excepted, 28. Theory of ore deposits, 28. 

 Mineralogy^ and Economic Geology chiefly sciences of abnormal minerals, 28. 

 Unstable character of eruptive rocks, 28 ; their resemblance to chemical labora- 

 tories, 29 ; passage from unstable towards more stable chemical combinations, 29. 

 Induration not always an indication of exposure to heat, 29. The glassy state of 

 rocks is neai'est their primitive condition, 29. Designations employed for the 

 three classes of rock-forming minerals, 29. Distinction of cases of envelopment 

 from alteration products, 29, 30. Application of the principles of Thermo-optics, 

 30. The pyrognostic characters of a mineral have little or nothing to do with its 

 condition before its formation, 30. The conditions under which minerals crystal- 

 lize from a cooling magma are different from those under which vein and altera- 

 tion minerals are formed, 30. 



SECTION IV. 

 Chemical Analysis of Rocks 31, 32 



Chemical Analysis unable to determine the mineral constituents of rocks, 31, 

 32. While Chemical Composition remains nearly constant, great variation exists 

 in the structure and mineral constituents, 31. What Chemical Analysis can Jo 

 for the lithologist, 31. Relation of Chemical Analysis of normal rocks to rock 

 species, 32. Analyses should be written in terms of the elements, instead of their 

 compounds, 32. 



SECTION V. 



Classification based on Mineral Composition 33-45 



Basis of the common classifications of rocks, 33 ; minerals used, and data re- 

 quired, 33. — The Feldspars, 33-43. Their different modes of origin, 33. 

 Scheerer's feldspar theory, 33, 34; Delesse's views, 34; Her.maxx's molecuhir 



