QUATERNARY AGE. — RECENT PERIOD. 557 



along rivers and about lakes ; drift sands or dunes ; glacial drift, like 

 that of the Glacial period, but more local. 2. Marine. — Estuary and 

 delta formations ; sea-beach accumulations ; off-shore deposits of de- 

 trital material carried into the ocean by rivers, or made from the 

 battering of cliffs by the waves ; deep-sea deposits of fine detritus. 



Of Chemical Origin. — Stalactitic and stalagmitic accumulations 

 in caverns (p. 75), the latter often covering the floors of caverns to 

 a considerable depth, and enveloping relics of their former inhabitants ; 

 travertine deposits (concretionary limestone), from streams holding bi- 

 carbonate of lime in solution, as along Gardiner's River, in the Yellow- 

 stone Park, and at Tivoli, near Rome (p. 75); siliceous deposits of 

 hot springs, as those of Yellowstone Park, and, with these, silicified 

 wood, leaves, insects, etc. ; deposits of bog-iron ores in marshes, with 

 often iron-ore fossils of fruits, stems, etc. 



Of Organic Origin. — Peat beds, or swamp formations of vege- 

 table character (p. 616) ; deposits of shells and shell-limestone in 

 lakes, or on seashores ; coral-reef formations in the warmer oceans, 

 often full of fossil corals and shells, but of existing species (p. 620) ; 

 chalky deposits of Rhizopod shells, over the ocean's bed, at various 

 depths down to 15,000 feet ; siliceous deposits, consisting of Diatoms, 

 or of these and the spicules of Sponges, either in fresh water, or in 

 the ocean. 



Of Igneous Origin. — Lavas, and other rocks of igneous ejections, 

 either from volcanoes or through fissures, comprising both dolerytic 

 and trachytic kinds. The great beds of dolerytic rocks which form 

 a table-like covering over parts of the Drift of the Sierra Nevada, 

 and other great streams of doleryte in the Snake River region, are 

 among the formations of the Recent period, besides the eruptions of 

 various volcanoes. 



The formations here enumerated are not always distinguishable 

 from those of the Champlain period, even in Drift latitudes, and much 

 less easily, or not at all so, from most of those outside of these 

 latitudes. The shells and corals afford no means of distinction, 

 except on certain coasts, where there has been a change of oceanic 

 temperature ; but remains of Mammals, and especially relics of Man, 

 when these are present, sometimes afford assistance. The seashore 

 beds may be at the water's level, or they may exist at different levels 

 above it ; yet it is generally, though not always, easy to separate 

 the elevated Champlain Drift deposits from the Recent, by the peculiar 

 structure of the sand accumulations and their geographical distri- 

 bution. 



H. Reindeer and Modern eras in North America. 

 The Recent period is separated from the Champlain, by an elevation 



