DRAINING. 



69 



peth in England ; and on the Forth and Clyde in Scot- 

 land. In Ireland, in Leitrim and Kilkenny, &c. 



Basalt, though an argillaceous rock, imbibes water 

 into its substance, and parts with it slowly. It decom- 

 poses chiefly into an ochry earth, which is loose and 

 porous on the hills ; but in the deep bottoms, forms a 

 strong loam upon clay. Antrim in Ireland, the Ochil 

 nnd Campsie Hills, and some of the western isles, are 

 the chief basaltic countries. The castle rock of Edin- 

 burgh, and neighbouring hills, may be also noticed. 

 The basalt hills are noted for abounding in springs, 

 which descend through their upright fissures, and are 

 thrown out by the clay at their bottom. 



Of the alluvial strata. Clay is an important member, 

 and forms the chief material by which other strata are 

 rendered impervious to water. When exposed, how- 

 ever, to continued drought, it slirinks, and cracks some- 

 times to great depths, thereby admitting water after- 

 wards to penetrate it with comparative ease. Clay, 

 therefore, is of itself not so thoroughly impervious, as 

 when duly mixed with sand, gravel, or loam, which 

 prevent it from shrinking to so great an extent. 



Graccl of every description, from its open nature, is 

 the most effectual of all conductors of water, at least 

 when free from the admixture of earthy matter; for in 

 this state it seems to aid the retentive nature of the 

 loam, a mixture of it being frequently preferred for 

 puddling hydraulic works. Where an open gravel is 

 covered with strata of clay or earth, it is one of the 

 most common causes of springs and watery land, the 

 cure of which shall be treated of hereafter. 



Sand being formed of smaller particles than gravel, 

 differs from it only by the slowness with which the wa- 

 ter passes through, and the greater height to which the 

 capillary attraction makes it rise. In other respects, its 

 properties are similar to those of the sandstone rocks 

 already described. 



Loam varies according to the substances with which 

 it is combined ; but in general may be considered as re- 

 tentive of moisture, at least after it is once thoroughly 

 saturated and puddled, to use the technical phrase of 

 drainers. 



Moss-peat, or Bog, is of two kinds. The flow moss 

 or red bog of Ireland, is a fibrous mass, composed of 

 undecayed vegetables of the moss kind ; it retains wa- 

 ter like a sponge, by capillary attraction, and after drain- 

 age, shrinks and compresses considerably. The other 

 kind is that called black bog, in which the vegetable 

 fibre of the mosses has undergone a certain degree of 

 decomposition. This substance, though light, is totally 

 impervious to water, and is frequently used in hydrau- 

 lic operations for puddling, where good loamy earth or 

 the like is not to be had. But after peat-moss has been 

 broken up and pulverised by cultivation, it permits the 

 water freely to percolate, insomuch that the upper 

 parts of the ridges, especially when they are much rai- 

 sed, are apt to have the crops fail on them during the 

 slight droughts of summer. Dried peats are quite im- 

 pervious to water. 



Having thus described the varieties of strata, and soils 

 produced from them, we shall proceed to consider the 

 effects of their various arrangement. 



CLASS I. Impervious Soils. Clay, or heavy Loam' 



Case 1 st, With Impervious Subsoil and Bottom. 



EXAMPLE. Deep strong clays, 8fc. In this case, 

 the rain water, after saturating the surface, being 



Draining. 

 Draining of 



precluded from penetrating farther, can only get away 

 by the slow process of evaporation. The soil is there- 

 fore continually moist and drenched during win- impervjous 

 ter. Cattle passing over it poach the surface, and fill so iis, with 

 it with numerous cups or holes, from which the water impervious 

 cannot escape even though the surface have a consi- subsoil and 

 derable fall. The spring shoot of grass is late ; the pro- 

 duce in wet summers is rank and coarse. On the other 

 hand, in dry summers, the moisture is rapidly diminish- 

 ed; and as no supply can arise from the subsoil or bot- 

 tom, the surface dries and hardens, cracking into gaps, 

 which allow free admission to the sun and air, so at to 

 scorch up almost every plant that is sowed upon it. 



In tillage, it is heavy and difficult to work, is crop- 

 ped with uncertainty, and the semifluid clay, while the 

 crop is young, is liable to close upon the roots of the 

 plants, and suffocate them by cutting off the supply of 

 air. The best account of this case, and means to be 

 used for its cure, are those given by Dr Anderson ; we 

 shall give it in his own words. " These soils are usu- 

 ally in themselves naturally fertile when drained. It 

 were to be wished that some less expensive mode of 

 doing so were discovered than that practised in Essex, 

 where they make covered drains of 2^ feet deep, run- 

 ning diagonally through the field at the distance of 

 twenty feet from each other, or in every furrow. The 

 wetness of this kind of land is not occasioned by springs, 

 but originates entirely in the proper waters of the site, 

 or what immediately falls upon it from the clouds. In 

 copious rains, a part of the water finds its way along 

 the surface into the furrows, if such have been made, 

 and by which it will be carried off the field ; but a con- 

 siderable portion also sinks down into the porous soil 

 on the top, until it reach the solid bed of clay below, 

 which never having been stirred or opened effectually, re- 

 sists the passage of the water, so that it can penetrate 

 downwards no farther. In consequence of this, it must 

 force its way laterally towards the furrows through the 

 upper mould ; or if no furrows are provided to carry 

 it offj it must gorge up the soil, and remain as in a ba- 

 son, in which the superficial soil is mixed with the wa- 

 ter in a thin paste, which remains of a soft consisten- 

 cy during wet weather, and in that state must be ex- 

 tremely injurious to the vegetation of plants. 



When the dry weather returns, the sun and air 

 will evaporate it, when the soaked paste, now deprived 

 of its moisture, assumes a hard irony consistence, equal- 

 ly unfit for the sustenance of plants as in its moistened 

 state. Such being the cause of this disease, the conse- 

 quences may be easily removed. ' The opening of hol- 

 low drains running diagonally across the slope at a 

 small distance from each other, if they can be kept open, 

 will answer the same purpose nearly that the drawing 

 of open water furrows would have done, and will doubt- 

 less mitigate the evil in proportion to their nearness to 

 each other ; but they must be very close together in- 

 deed if they remove it entirely ; for still the soil must 

 be drenched in the same manner as before, by the 

 water forcing its way through it until it reaches the 

 drain. 



Now, as the rain water will sink perpendicularly 

 through the soil until it meets with the solid clay before 

 it attempts to seek a lateral direction, it must follow, 

 that the lower part of the mould, or that nearest the 

 clay, will be more drenched with water than those parts 

 of it which lie at a greater distance above the clay. Of 

 course, the deeper the soil the less will the surface 

 mould be liable to be drenched with hurtful moisture ; 

 hence it follows, that if the soil shall be deepened to 



