154 DYNAMICAL GEOLOGY. 



bottom from its lower dying surface; for tlie moss lias the property of 

 dying at the extremities of the roots as it grows above. It thus gradually 

 takes possession of the pond, and may form beds of great thickness. 



In some limestone regions, the Sphaguous mosses are replaced by species 

 of Hypnum, as in Iowa. The leaves and stems, branches and stumps, of 

 trees and shrubs, growing over the marshy region or in shallow waters, and 

 any other vegetation present, contribute to the accumulating bed. The fresh- 

 water shells growing in the waters, and the spicules of any sponges, with 

 the insects, and the carcasses and excrements of animals become included. 

 Earthy material also may be blown over the marsh by the winds, or brought 

 by inflowing streams. 



In wet parts of Alpine regions, there are various flowering plants which 

 grow in the form of a close turf, and give rise to beds of peat, like the moss. 

 In Fuegia, although not south of the parallel of 56°, there are large marshes 

 of such Alpine plants, the mean temperature being about 40° F. On the 

 Chatham Islands, 380 miles east of iSTew Zealand, peat thus formed has 

 a depth of 50 feet. 



The dead and wet vegetable mass slowly undergoes a change in its lower 

 part, becoming brownish black, loose in texture, and often friable, although 

 commonly penetrated with rootlets. The change is sometimes continued 

 until coal is formed ; but unlike good coal it still contains usually 25 to 33 

 per cent of oxygen. 



Peat-beds cover large surfaces of some countries, and occasionally have 

 a thickness of 40 or 50 feet. The rate of growth varies with the amount of 

 vegetation, moisture, and other conditions ; a foot in depth may form in five 

 to ten years. One tenth of Ireland is covered by them ; and one of the 

 " mosses " of the Shannon is stated to be 50 miles long and two or three 

 broad. A marsh near the mouth of the Loire is described by Blavier as 

 more than 50 leagues in circumference. Over many parts of Kew England 

 and other portions of North America, there are extensive beds, almost every 

 old marsh having more or less peat below. The amount in Massachusetts 

 alone has been estimated to exceed 120,000,000 of cords. The Dismal Swamp, 

 10 miles by 30 in area, situated on the borders of Virginia and North Caro- 

 lina, is for the most part a region of very deep peat. 



Peat-beds sometimes contain standing trees, and entire skeletons of ani- 

 mals that had sunk in the swamp. The peat-waters have an antiseptic 

 power, and consequently tend to prevent complete decay of the vegeta- 

 ble matter of the peat-bed. Plesh is sometimes changed by the burial 

 into adipocere. 



Peat is used for fuel, and also as a fertilizer. When prepared for burning, it is cut into 

 large blocks, and dried in the sun. It is sometimes pressed, in order to serve as fuel for 

 steam-engines. Muck is another name for peat, especially for impure kinds, when em- 

 ployed as a manure ; any black swamp-earth consisting largely of decomposed vegetable 

 matter is so called. 



Beds of marine plants in the rocks of littoral regions are almost unknown. Specimens 



