128] A TOPOGRAPHICAL 



ness of clay. Different proportions of these four earths will form 

 soils of every degree of dryness or moisture, and their fertility is 

 derived from carbon : dung-hill water contains much carbon. A 

 fertile soil should contain one-sixteenth its own weight of carbon, 

 but it must exist in the soil in a particular state of combination to 

 promote fertility ; it must be in a state to be soluble in water. 

 Manures, on putrefaction, part with their carbon, which is absorbed 

 by the soil, and by the plants growing thereon. 



Mr. Keir conceives that the coarse bluish clay-soil of Rowley 

 is principally decomposed rag-stone, which stone, from its analysis, 

 is of the kind called basaltes or trapp : it first decomposes into a 

 reddish powder. Marl is clay mixed with carbonate of lime ; sand 

 consists of small grains of siliceous stones, not cohering nor softened 

 by water ; clay-soils are formed of common clay mixed with de- 

 cayed vegetable and animal substances. Loam, not cohering so 

 strongly as clay, is of several varieties : the stiff, strong, heavy 

 loam, is composed of clay and coarse sand ; calcareous loam is a 

 mixture of lime, clay, and coarse sand, the lime predominating ; 

 sandy loam, the same ingredients, the sand predominating to eight 

 or nine-tenths of the whole. Thus are all the upland soils formed 

 and composed, and by degrees impregnated with carbon by 

 vegetation. 



Peat-earth, or the meadow and lowland soils, have been formed 

 by the decomposition of aquatic vegetables, root and branch, 

 mixed and impregnated with earthy particles, brought from the 

 upland by wind and water, during a long course of succeeding 

 ages. 



The mineral clays of this country are a mixture of alumina and 

 silica, the alumina in powder, the silica in small stones : besides 

 these, clay often contains lime, magnesia, and oxyd of iron. The 

 varieties are common brick-clay, potter's-clay, indurated clay, and 

 shistose clay, the latter found in strata in coal mines, and when 

 impregnated with bitumen, called shale, roach, and clunch, by the 

 miners. 



The aggregates of stone are small grains of sand, consisting of 

 quartz, flint, hornstone, siliceous shistus, felspar, and mica, all or 

 in part cemented by lime, alumina, silica, and iron. 



The southern part of Staffordshire, to a great extent, contains 

 valuable mines of coal, iron-stone, lime-stone, and clay, to which 

 are owing the foundation and prosperity of the populous villages 

 of this part of the county, and of the neighbouring towns, Bir- 



