Page images
PDF

prejudices of many geologists; therefore some will find fault even if the work could be well done.

I would wish to impress on my readers that this book has been written as a reference for surveyors and students while engaged in the field. Should they desire a perfect knowledge of rocks, they must study the various papers and works of the different eminent Petrologists. The work, necessarily, is far from perfect: still I hope it may be of some small use or help to learners of Geology.

During the compilation of this Manual, the writings of numerous Petrologists have been consulted and quoted; also works on general subjects from which information could be procured. Dana's suggestions as to the termination of Rock names have been adopted as far as practicable, while the older names for rocks are generally adopted, except when they are objectionable or better names have since been proposed. Such local names as were known are also given, as they may assist explorers in gleaning information about a country. To various fellow-labourers I am much indebted: to D. Forbes, F.R.S., &c, for information; also to W. King, Dep. Supt. Geol. Surv., India, and for his valuable assistance while arranging and classifying the rocks. I should also mention the names of the Rev. M. H. Close, M.R.I.A., &c.; Stackpoole Westropp, M.D., M.R.I.A., &c.; and H. Leonard, M.R.I. A.; besides others who have supplied me with lists of local names.

G. H. K.

CONTENTS.

Preface ... Page iii

Introductory Remarks 1

Part I.—Classified Table Of The Rocks 9

Order I. Ingenite Rocks... ... ... ... ... 9

Class 1. Granitic Rocks 9

Class 2. Plutonic Rocks 10

Class 3. Volcanic Rocks ... ... ... ... 14

Class 4. Transition or Metamorphic Sedimentary Rocks 15

Order II. Derivate Rocks 19

Class 1. Subaqueous Rocks ... ... ... ... 19

Class 2. Subaerial Rocks 24

Part II.—Order I. Ingenite Rocks 26

Class 1. Granitic Rocks 26

Group A. Intrusive Granite ... 27

Group B. Granite for the most part non-intrusive 32

Group C. Protogene... 36

Group D. Elvanyte 39

Class 2. Plutonic Rocks 43

Group E. Felstone 44

Group F. Whinstone ... 55

Group G. Rocks due to pseudomorphic action ... 63

Group H. Tuff 66

Class 3. Volcanic Rocks 69

Group I. Trachytic 70

Group J. Augitic 73

Group K. Tufa and Peperino 75

Class 4. Transition Rocks 76

Group L. Gneiss ... 77

Group M. Schist 80 Group N. Slate ... Page 88

Group 0. Calcareous Rocks ... 89

Group P. Pseudomorph Calcareous Rocks ... 90

Part III.—Order II. Derivatb Rocks 94

Class 1. Subaqueous Rocks 94

Group A. Rocks for the most part mechanically

formed 94

Subgroup A. Arenaceous Rocks ... ... 95

Subgroup B. Argillous Rocks 99

Subgroup ft Fault-rock 106

Group B. Rocks for the most part chemically formed 106

Subgroup .4. Haylyte ... 107

Subgroup B. Gypsum 107

Subgroup C. Anhydryte ... ... 108

Subgroup D. Dolomyte ... ... ... ... 108

Subgroup E. Quartz , 108

Subgroup F. Limonite Rock 109

Subgroup G. Hematite Rock 110

Subgroup if. Spherosiderite ... ... ...110

Subgroup J. Minerals occurring as Rock Masses 111 Group C. Rocks partly mechanically, partly chemically, and partly organically formed ... ... 112

Subgroup^. Laminated Coal ... - 112

Subgroup B. Limestone 115

Subgroup ft Dolomyte ... 120

Class 2. Subaerial Rocks ... 122

Group D. Mechanically, chemically, and organically
formed

122

Subgroup A Coal 122

Subgroup B. Surface Deposit and Accumulations 126

HAOT)Y-BOOK OF KOCK NAMES.

INTRODUCTORY REMARKS.

THE term Rock, in a geological sense, includes every solid substance that is an ingredient, or forms part, of the earth. Thus loose sand, clay, peat, and even vegetable mould, geologically speaking, are rocks. Jukes thus defines a rock :—" A mass of mineral matter consisting of many individual particles, either of one species of mineral, or of two or more species of minerals, or of fragments of such particles. These particles need not at all resemble each other in size, form, or composition; while, neither in its minute particles, nor in the external shape of the mass, need a rock have any regular symmetry of form." Rocks are most variable in condition and structure; soft or hard, loose or compact, friable or tenacious, coarse or fine, crystalline or homogeneous; or they may be scoriaceous, vesicular, hyaline, &c. &c.

Rocks may be chemically, mechanically, or organically formed, or two or more of these combined; they may be stratified or unstratified, igneous or aqueous, or partaking of the nature of both. Various classifications have been adopted by different writers on the subject, each taking different peculiarities as a foundation for his system. Jukes and others have divided rocks into four classes; namely, Igneous, Aqueous, Aerial, and Metamorphic; while Forbes, who wrote subsequently, has simplified this division, and makes two great classes of all rocks.

Forbes calls his first class by the names Ingenite or Subnate Rocks; i.e., "such as are born, bred, or created within or below;" and the second he calls Deeivate Rocks, "since directly or indirectly they are all derived from the destruction of the former."

Under Ingenite rocks are included all the true igneous, intrusive or irruptive rocks, whether they are still in their original state, or whether they have been subsequently affected by metamorphic action, as also the metamorphosed sedimentary rocks; since all these have been bred or formed within or below the surface of the earth. Thus all granites, whether truly igneous or metamorphic,* are included. The Derivate order consists chiefly of sedimentary rocks, but it will include some, such as Dolomyte,-)- Halyte, &c, which some authorities refuse to regard as sedimentary rocks.

In this Manual these suggestions will be followed, and the rocks classed in two orders; namely,

i * Some authorities deny that any granite can be of metamorphic origin. To me, however, there does not appear to be any room for doubt, for in different places I have found granite graduating through gneiss and schist into unaltered rocks.

t Dana suggests that all rock names ending in ite should be changed into yte, and the first termination should be kept solely for minerals. A general adoption of this suggestion would prevent the confusion that at present exists when so many rock masses and minerals have similar names,—such as Augite, Steatite, &c. &c. Danas names for the minerals are those that will be used in this Manual.

« PreviousContinue »