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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.

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THE term Rock, in a geological sense, includes

I 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 DERIVATE 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,

* 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.

+ 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 pames,—such as AUGITE, STEATITE, &c. &c. Dana's names for the minerals are those that will be used in this Manual.

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