viii CONTENTS. 



theory, 34. Waltershausen's theory, 34. Krablite a rock, and not a mineral, 34, 

 35. Eunsen's view of Baulite, 35. Hunt's theory of the feldspars, 35. Tscher- 

 mak's theory, 35, 36 ; Streng's views, 36 ; Petersen's objections to Tschehmak's 

 theory, 37. Dana's method of accounting for variations in feldspars, 37. 

 Hunt claims to have originated Tschermak's theory, 37. Hunt's alteration of 

 his direct quotation, 37. Hunt's theory not original with him, and not the 

 same as Tschermak's, 37. Writers who through misapprehension have acknowl- 

 edged Hunt's claims, 37, 38 ; Silliman charges Tschermak with appropriation of - 

 Hunt's views, 38 ; Leeds recognizes the difference between the views of Hunt and 

 Tschermak, 38. The charges of appropriation made against Tschermak false, 38. 

 Descloizeaux on the optical properties of the feldsjiars, 38 ; Friedel's theory 

 of their chemical constitution, 38 ; Vom Ratu's views, 38, 39. Descloizeaux's 

 discovery of microcline, 39. Mallard and LiivY teach that it is the same as or- 

 thoclase, 39. Schuster's observations on the optical properties of the feldspars, 

 39. Feldspars not suitable to found specific distinctions upon, 39. No means 

 of positively determining the feldspar species in rocks, 40. Descloizeaux's 

 method of determining feldspars, 40 ; Pumpelly's modification of, 40, 41 ; Pdm- 

 PELLY anticipated by Levy, 41. Tlie work of both independent, 41. Hawes on 

 the distinction of feldspars, 41. Boricky's micro-chemical method, 41, 42. 

 SzABo's method, 42. Geo. H.' Emerson's invention of a method of distinguishing 

 minerals by means of crystals formed in blowpipe beads, 42 ; amplified later by 

 GusTAV Rose, W. A. Ross, and H. C. Souby, 42. Tlie specific gravity method for 

 determination of the feldspar species, 42. Objections to the above methods, 42, 

 43. The twinning not constant in feldspars, 43. The chief value in lithology of 

 the determination of the feldspars, 4.3. — The Pyroxene-Amphibole Groups, 44, 



45. A variaVile series in them as in the feldspars, 44. Cleavage not a satisfac- 

 tory basis for separating Diallage from Augite, 44. Augite found iu Basic and 

 Acid Rocks, and in the older and younger, 44. Alteration of Augite, 44. Sec- 

 ondary origin of some Pyroxenes, 44. Relation of Hornblende and Augite, 44. 

 The same hand specimen both a Diorite and Diabase, 44. The Mica Series, 45. 

 Secondary origin of Chlorite and Epidote, 45. — Mineralogical Nomenclature 

 OF Rocks. Rock Classification based on mineralogy alone, impracticable, 45, 

 Rock Structm'e valueless for specific distinctions, 45. 



SECTION VI. 



Naming Eocks according to the Geological Age 45-47 



Such nomenclature not natural, 45. No line can be drawn at the Tertiary Age, 



46. Alteration under like conditions proportionate to age, 46. The petrogra- 

 pher's duty, 46. The presence of Fluid Cavities in rocks, 46. Vogelsang and 

 JuLiEN on Fluid Cavities, 46. Fhud Cavities sometimes original and sometimes 

 secondary iu rocks, 46. Occurrence in Tertiary Rocks, 46. The cause of the 

 Crystalline Structure in the older rocks, 46, 47. The Granitic Structure, 47. 



SECTION VII. 



Methods of Classification 47-51 



Classification the framework of any descriptive science, 47. The mineralogical 

 method of studying rocks, 47. The natural method, 47. The relation of miner- 

 als to rocks, 47, 48. Meaning of the Natural Classification, 48. Characterization 



