C8 



DRAINING. 



i -o -. 



>l*!e rocks. 



mining. r<\ hy water* derived from higher grounds ; an<l of 

 ""Y"""- swallow*, which absorb or convey them nil' to lowrr. 

 These have, in many cases, an important i I'ivt on the 

 Mperinciunl>eiit soil, mid their drainage is frequently 

 accessary for improving the lain! ; but it requires a par- 

 ticular mode of in." t, which shall In- dc-cribed 

 under a succeeding head. 



Like the soil and subsoil, we mny also class tin 

 rious kind* of bottom into the jmrous and imporviou* ; 

 this Ix-ing the most important distinction in the eye of 

 the drainer. Hut it may not be imprujn-r to be some- 

 what more particular in distinguishing the more re- 

 markahlt . >f the strata of the earth, which will 



give us a Ix-tter idea of the qualities of the varioi: 

 and sub-oils, it Ix-ing from the decomposition of the 

 former that these last are formed. 



The crystallized mountain rocks such as granite, &c. 

 seldom occur in situations fit for the labours of the agri- 

 culturist ; it may be only observed, that having no fis- 

 sures, they are impervious to water. They decompose 

 into a sharp sand, which is one of the readiest conduc- 

 tors of water we have ; and when covered by a clayey 

 or loamy soil, and well drained, form valuable lands, 

 producing great crops of potatoes and barley. The 

 chief granitic soils are in Cornwall, part of Leicester 

 and CumlM-rland, in England ; in Galloway, Aberdeen, 

 Row, and much of the Highlands of Scotland ; in Do- 

 negal, Galway, Wicklow, and Down, in Ireland. By 

 far the greater part are moors covered by fibrous n. 



The various kinds of slate rock are composed chiefly 

 of clay ; and are therefore impermeable to water, ex- 

 cept in their cracks and fissures, which, near the sur- 

 face of the earth, are numerous. The strata or plates 

 stand usually on edge, so that the water easily finds its 

 way down into them, and, splitting the rock by its hy- 

 drostatic pressure, works by degrees the surface into a 

 clayey loam. L'nder this the water sinks until direct. 

 ed to the surface by closer strata ; and then forms 

 springs, or watery land, according as it is in greater 

 or less quantity. The ridges of the slate rocks running 

 parallel for great distances, form narrow hollows, which 

 are sometimes lakes, sometimes fibrous mosses, and can 

 only be drained with effect by cross-cutting the strata. 

 The ridges, on the other hand, are usually dry and fer- 

 tile. This kind of rock occupies a great extent of these 

 kingdoms, being found in Cornwall and Devon, most 

 nf Wales, Lancaster, Cumberland, and Westmoreland. 

 In the Highlands of Scotland, all the south and south- 

 east of Ireland, and in a band which runs from the 

 ehire of Berwick across the channel to the banks of the 

 Shannon ; as also in Deny, Donegal, and part of Mayo. 

 There are, however, many varieties, the best and hard- 

 est slate being nearly impervious to water, and keeping 

 the lands above them dry and sharp. The softer again, 

 or shales, imbibe water in considerable quantity, and, 

 parting with it slowly, keep the land above them con- 

 stantly moist and cold. 



The sandstone rocks of every kind are more or less 

 porous, and transmit the water through their substance 

 like a filter. They are found in great abundance in va- 

 rious parts of the kingdom. Often occupying the ri- 

 sing grounds, and usually of a reddish cast, the soil 

 produced from them is dry, and, though meagre, not 

 always unfertile. But the water passing through them 

 frequently acquires a mineral impregnation from iron 

 pyrites, which enables them to preserve vegetable mat- 

 ter from decay. From this cause we may account for 

 the numerous bogs or mosses which disfigure the base, 

 banks of the sandstone hills, where water is fre- 



quently oozing, and the Itottoms of the deep 

 trict-, from whicli it has not a ready passage. Tlie 

 most effectual cure for it is draining t the 



cruise ; and calcareous earth to free the water of il- t-.n- 

 ti-eptie property, by neutralizing the contained acid*. 



The green-tone, and green conglomerate or porplu- ivrphrriuc 

 ril'c rocks, produce l>\ their decomposition 

 cccdiiigly fertile. Tlie liner | imes a limni : 



the larger pebbles form an open substratum : the rock 

 itselt' i- generally close and retentive, though capable 

 of imbibing a considerable proportion into it- -uhst 



The calcareous rocks lire very variou- in texture. 

 'Ill'' softer and gratuitous kinds, as the chalk in the 

 south and east of England. The oolite of Bath, the 

 cotcswold, \c. is of a porous and absorbent nature, and 

 imhilxs the rain into its substance as fa-t a- it tails. 

 The water descends, as in n filter, still more readily 

 than in sandstone rocks, until it come to an impervious 

 stratum, bv whicli it is conducted into the sea, or thrown 

 out on the surface in the form of springs. The chalk 

 is only found to the eastward of a line from Dorchester 

 ulerland. 



Tlie harder kinds of chalk and limestone, though Chdk ixl 

 iu thcirtextureinthc individual specimen, are usu- limestone, 

 ally, in the great scale, divided by numerous chasms and 

 fissures, some of them opening into enormous caverns, 

 of whicli those in Derby, and in many parts of Ire- 

 land, are very striking instances. This kind of rock, 

 where uncovered by oilier soil, is consequently as free 

 a conductor of water as we know ; even large subter- 

 raneous rivers sometimes pass through it. The most 

 striking example in these kingdoms is perhaps that of 

 Lough Mask, in the west of Ireland, where the water-i 

 of a bason, of 250 square miles, pass for two miles un- 

 der ground into Lough Corrib. Many such basons are 

 alternately dry land and fresh water lake, according as 

 the supply is less or greater than can be conveyed 

 through the syphon, which forms their outlet. The 

 Cirknitz Sea in Austria is of this kind : Sec CIKKMTZ. 

 Such lakes are named Furloughs, i. e. I.andlakes, in 

 Ireland, and are very common in Connaught. There 

 Furlough More, near Gal way, covers an extent during 

 v inter of several thousand acres. 



Another sort of limestone is the magnesian, or water Magncmaa 

 lime, occurring at shallow depths, and bedded in clay, lim- 

 it is particularly remarkable for making lime, which 

 will s(tand harden under water; so that when applied 

 to land, it has just the opposite effect of common lime, 

 as far as drainage is concerned, binding and consolida- 

 ting the soil, instead of opening it. 



The limestone strata occupy a great extent of these 

 kingdoms, particularly in England and Ireland. One 

 great field runs from Berwick to Lancashire and Derby- 

 shire. The chalk also occupies most of the south and 

 cast of England ; and, in Ireland, the greater part of 

 Leinstcr and Connaught is a lime-tone country. There 

 are also many -mailer tracts. There is but little lime- 

 stone in the north of Scotland, though it abounds in 

 the middle or lowland tracts, forming usually the ba- 

 son of the coal strata; as is likewise the case along the 

 Severn. The magnesian lime begins at Sunderland, 

 running southwards through the middle of England, 

 and turning off towards the Bristol Channel. 



The coal strata are very various. The coal itself is Cosl ttrau. 

 porous. The chinch shale or till impervious, being 

 chiefly clay, and well adapted to cure the defects of the 

 deep saiidv soils. Tlie coal sandstones are usually some- 

 what argillaceous, and consequently not infertile. The 

 greatest tracts of coal country are from Bristol to Mor- 



