

782 • DYNAMICAL GEOLOGY. 



or spathic iron),which are the sources of the iron of the world, a small part of the iron 

 carbonate (which occurs in veins) excepted. Hematite and magnetite occur in meta- 

 morphic rocks ; hematite, limonite, and siderite, in non-metamorphic. 



2. Copper ore in the form of malachite, azurite, cuprite, chalcopyrite, and sometimes 

 tetrahedrite, in the Permian of German}' and Russia. 



3. Auriferous and platinum gravel deposits (the source of a large part of the gold of 

 commerce), which are merely gravel beds, like any other gravel of the stratified drift, 

 but made from rocks that were intersected by veins of gold-bearing quartz. 



Minerals have their natural associations, and the study of these — or the paragenesis 

 of minerals — has great geological importance. But it leads off into the broad subject 

 of chemical geology, which is of extent enough to fill several volumes. 



The most important descriptive work in connection with the subject of mineral veins 

 which has appeared in the United States is the report on the great Nevada Mining Re- 

 gion, published as Vol. III. of the Reports of the U. S. Geological Exploration of the 

 40th Parallel, under the title, Mining Industry, by James D. Hague, with Geological 

 contributions by Clarence King, 4to, 1870. 



J. D. Whitney's Metallic Wealth of the United States (8vo, 1854), is an excellent 

 work, much needing a revision bringing it down to the present time. 



R. W. Raymond's Reports to the Government On the Mineral Resources West of 

 the Rocky Mountains, 1869 to 1876, contain a large amount of information on the mines 

 of the country, though treating mainly of resources and mining operations. # 



De la Beche's more important works are his Report on the Geology of Devon and 

 Cornwall, and the Geological Observer; the last edition of the latter appeared in 1851. 

 The Transactions of the Geological Society of Cornwall contain many valuable me-, 

 moirs on veins, among which those of J. W. Henwood, in Vol. V. (1843), have special 

 interest. The titles of the works of A. Daubr^e and Bischof, referred to in the pre- 

 ceding pages, are given on pages 769, 770. The excellent treatise on Ore Deposits, of B. 

 Von Cotta, translated by Professor Frederick Prime, Jr., from the 2d edition (but with 

 additions and emendations by the author), was published in New York in 1870. 



VI. THE EARTH A COOLING GLOBE: ITS CONSE- 

 QUENCES; OR CAUSES AND EFFECTS OF MOVE- 

 MENTS IN THE EARTH'S CRUST. 



1. ACTUALITY OF CHANGES OF LEVEL. 

 All geological history testifies against the stability of the rocky 

 crust of our globe ; and if the earth has cooled from fusion, as is be- 

 lieved, abundant reason for this unstableness exists. The effects reach 

 backward to unknown limits, and downward beneath other agencies 

 of change. They include indefinite grades of variation in level, up 

 to the making of mountains and continents and the deepening of the 

 oceanic depressions, besides, also, the fracturing, faulting, and upturn- 

 ing of rock formations ; and they embrace, indirectly, the crystalliz- 

 ing of sedimentary strata, the making of veins, the opening of vol- 

 canic vents, and the determining of variations in climate, in faunas, 

 and in living species. 



The following facts are here stated anew, to bring to view the reality and extent of 

 changes of level. 



