X.] ALLUVIAL LOAMS 279 



drying to hard clods; an admixture of coarser sand 

 results in a better texture. The loams are typical 

 soils of arable cultivation and are suitable to all crops ; 

 their manurial requirements vary with the origin of 

 each soil, and are largely conditioned by its poverty 

 or richness in calcium carbonate. While no special 

 flora can be associated with the loams, there are several 

 weeds generally taken as indicative of good fertile soils 

 of this class; such are chickweed (Stellaria media), 

 groundsel (Senecio vulgaris) , fat hen {Chenopodium 

 album)) stinking mayweed (Antkemis Cotula), and 

 the Sow thistle (Sonchus oleraceus). Other weeds 

 of cultivated land, which only occur when the soil 

 is capable of carrying fair crops, are goose grass 

 {Galium aparine), the speedwells {Veronica agrestis, 

 etc.), pimpernel {Anagallis arvensis), henbit (Lamium 

 amplexicaule\ wild poppy {Papaver rhaeas\ and the 

 small spurges like Euphorbia Peplus. The alluvial 

 soils which border the rivers and pass into con- 

 siderable marshes at their mouths, must, by their 

 texture, be classed among the loams, and present no 

 specific features, except where they are waterlogged 

 and marshy, or near the sea where the subsoil water 

 becomes so rich in salt as to alter the character of 

 the vegetation. The marshy patches accumulate, as 

 a rule, what has already been described as " mild 

 humus," owing to the presence of bicarbonate of lime 

 in the soil water; it is generally accompanied by 

 deposits of pulverulent ferric hydrate. The presence 

 of rushes, of sedges like the carnation grass, or orchids 

 like 0. maculata and O. latifolia y are characteristic of 

 these spots requiring drainage. Lousewort (Pedicularis 

 palustris) is said only to occur in marshes where the 

 water contains lime. 



The salt marshes possess a characteristic vegeta- 



