INTRODUCTION 57 



marin de Cernay, de Meudon. In the great Oligocene Bad Lands of South Dakota 

 it is most interesting to find the coarser sediments of a 'river channel' traversing 

 a fine 'overflow' deposit, each containing its characteristic forms of mannnahan 

 life. Both in the deposits of the mountain regions and plains regions of the western 

 United States great and small areas of these sediments occur containing either 

 weatherworn or often battered fossils. 2. Sandstones {"Gres," " Sa7idsteme") . 

 Composed chiefly of quartz sand or sometimes of feldspar grains (arkose sand- 

 stones), associated with deposits of volcanic origin, as in the Bridger Formation. 

 Sandstones, due to sea and river action, naturally cover wider areas than the coarser 

 conglomerates, which they often adjoin, because they display the transporting 

 power of slower water action or higher wind action, as in deserts. Characteristic 

 of late Pleistocene and Glacial times. 3. Shales (" Argile schisteuse," " Schiefer- 

 thon"). Chiefly fine mud sediments, deposited in still or comparatively still water 

 and exhibiting more or less perfect horizontal or oblique cleavage or lamination. 

 Often contain beautifully preserved leaves and remains of fossil fishes, as the Green 

 River Shales. Rarely contain remains of mammals. 4. Clays {" Argile,'' "limon," 

 " Thou"). Due to river, flood plain, or deep water action, these are uniformly fine 

 sediments, typically of continental origin, in large part a consolidated loess. The 

 true "plastic clay" or argile plastiqiie is mostly of marine origin and results from 

 the final decomposition of feldspar. The famous London Clay, containing Hyraco- 

 therium, is an estuarine formation. 5. Loess ("Loess" in French and German). 

 Characteristic of late Pleistocene and Glacial times. An unconsolidated, fine, porous, 

 silicious silt, deposited on river flood plains, in back waters, and by the agency of 

 the "wind on dryland surfaces and (according to some authors) as glacial mud. 

 Water-borne and wind-borne loess are hard to distinguish; some loess is of joint 

 origin. In some regions loess is composed of volcanic ash more or less altered by 

 weather and river erosion. Where of flood plain origin it may show horizontal 

 color banding, due to seasonal floods, or in aeolian loess to the direction of preva- 

 lent winds. A partially consolidated loess would be commonly called a clay; 

 when further consolidated, a shale. The most famous loess dejiosit is the Pampean 

 formation of Argentina, rich in mammals. 6. Volcanic ash and tuff ("Tufs," 

 "Tuff"). The great constituent of the Mountain Basin formations of North 

 America. Composed of volcanic ejecta, containing many feldspathic particles. 

 Where wind-borne, the ash resembles loess; where water-borne, volcanic ash forms 

 tuffs. Examples are large parts of the Bridger, Wind River, and other mountain 

 basin formations of North America. 7. Lignites {"Lignites" " Braunkohle") . 

 Rare as a Csenozoic formation in America, common in the Eocene of Europe, as 

 the Lignites du Soissonais, de la Debruge, de Cadibona. 8. Gypsum {"Gypse," 

 "Gyps"). Formed by evaporation of lagoons. Afford an invaluable indication of 

 climatic conditions. The most famous deposit of the kind is the Upper Eocene 

 Gypse de Montmartre, near Paris. 9. Limestones {"Calcaire, " "Kalk"). Limestones, 

 as the Calcaire grassier of the Upper Eocene of France, are chiefly calcareous (car- 

 bonate of lime), sometimes of organic origin, or formed by the accumulation of 

 shells ; sometimes by deposition from water holding lime in solution. Traver- 

 tines are calcareous deposits formed from hot springs. 10. Marls ("Marnes," 

 " Mergel"). Loose or unconsolidated deposits of earth, of lime, of shells, etc., rich 

 in organic matter. Phosphate Beds are marls or other formations rich in phos- 

 phate of lime, such as those of South Carolina; they are littoral and estuarine in 



