84 DYNAMICAL GEOLOGY. 



watchful observation. It is for this reason that geologi- 

 cal phenomena are peculiarly adapted to cultivate the 

 habit of observation. 



SECTION I. VEGETABLE ACCUMULATIONS. 

 Peat-Bogs. 



Definition. Every one knows that, under certain 

 conditions, especially a moist climate and imperfect drain- 

 age, and in certain spots where moss, rushes, and other 

 water-loving plants grow, there is found a black, carbona- 

 ceous mud, often many feet deep. A surface-crust Js 

 formed on the interlacing roots of many kinds of plants, 

 beneath which is a tremulous mass of semi-liquid matter. 

 On the surface-crust men or animals venturing, sometimes 

 break through, and are ingulfed and perish. Such car- 

 bonaceous mud is called peat, and the places where it 

 accumulates, peat-mosses or peat-bogs. 



Peat-bogs are most common in cool, moist climates. 

 A large part of Ireland, Scotland, Norway, Sweden, and 

 Northern Europe generally, is covered with them. They 

 cover, also, large parts of New England, and especially 

 of Canada. In California, though a dry climate, an im- 

 perfect peat is found, covering large areas on the Lower 

 Sacramento and the San Joaquin Rivers. These are the 

 " tule-lands." In tropic and semi-tropic countries, accu- 

 mulations of peat are not so common, but are on a grander 

 scale. The peaty accumulations there are overgrown, not 

 by moss and rushes and shrubs, but by great swamp-trees. 

 In these countries we have not so many peat-bogs, but a 

 few great peat-swamps. Examples of these are found in 

 the Great Dismal Swamp of Virginia and North Carolina, 

 and in the great peat-swamps of the river-swamp and delta 

 of the Mississippi. 



Structure and Composition of Peat. Beginning at 

 the surface, we have in a peat-bog first the living vegeta- 



