522 RECENT. 



has shown that marine organic remains, Sponge-spicules, tests of 

 Foraminifera, and fragments of Echinoderms, may be carried high 

 up an estuary and up rivers.^ 



The Alluvium where it approaches the sea is naturally of an 

 estuarine character, and the beds so formed are known as Scrobicii- 

 laria-c\^.y?,, etc. Much Alluvium is actually below the sea-level, 

 and is preserved only by artificial banks, or by natural barriers 

 of Blown Sand. The term Warp is sometimes applied to tidal 

 Alluvium. (See sequel.) 



Alluvial soils are generally fertile, forming rich meadow and pasture land. 

 The principal of these grazing-lands are situated on the banks of the Humber, 

 Trent, Great Ouse, Yare, Thames, and Severn, and they include the flats bordering 

 the Bristol Channel, in Somersetshire, and the Sussex levels. 



The Alluvial silty deposits are sometimes of economic value, sand from the bed 

 of the Thames being useful in brickmaking, while Portland cement has been made 

 from Chalk mixed with river-mud from the mouth of the Thames, and other 

 places. (See p. 419.) In some localities, as at Wells in Norfolk, bricks are made 

 from Alluvial clay. 



Peat. — Peat is an accumulation of vegetable matter, partly 

 mineralized, and of variable composition and consistency. It has 

 been formed in low-lying marshy areas of more or less stagnant 

 water, bordering rivers or lakes ; and it has been formed in pools 

 and marshy places on elevated moors and mountains. Hence it is 

 sometimes divided into Hill Peat, and Bog or Marsh Peat. In 

 many cases peaty beds in Alluvial deposits are derived from 

 accumulations formed elsewhere : where peat has been formed 

 in situ the beds are often termed Peat Mosses (or INIorasses). Near 

 the surface Peat is usually light-brown in colour, and spongy, while 

 the plant-remains are but little altered; deeper down the substance is 

 darker in colour, denser, and the plants are more decomposed ; in 

 places the Peat is quite black, and it is more or less earthy, 

 especially in the lower part. As a rule, however. Peat contains but 

 3 per cent, of earthy matter, which may have been introduced by 

 streams, and in some cases by wind ; the greater part of the sedi- 

 ment that might have been carried in by streams having doubtless 

 been filtered out by reeds and rushes that bordered the low-lying 

 tracts in which it was accumulated. 



Marsh Peat varies locally in composition, but is often formed to 

 a large extent of the Bog-moss {Sphagnu?n palustre), together with 

 Reeds {Arundo), Rushes {Jmiciis), Sedges {Carex), Ferns, and 

 other more or less aquatic plants. In places other mosses {Hypnii?n 

 Huitans and H. filiciftum), Stoneworts {Chara hispida and C. gracilis), 

 and the Bladderwort {Utricularia vulgaris) are important consti- 

 tuents of Peat. Stumps and prostrate trunks of Trees are some- 

 times met with at or near the base of the peat, in a more or less 

 rotten state, and occasionally penetrated by the roots of marsh 

 plants. These trees include the Oak, Scotch Fir, Alder, and Birch, 

 and more rarely the Ash, Hazel, and Willow. - 



Q. J. xxxix. 620. 



W. Carruthers, P. Geol. Assoc, v. 8. 



