FORMATION OF THE FRUIT AND KITCHEN GARDEN. 



19 



and at the same time naturally well drained. 

 Where there is a good top-soil on a loamy sub- 

 soil, and this again on gravel conducting to a 

 considerably lower channel, no artificial drain- 

 age will be required. The worms will perforate 

 the stratum of loam, even if it should be 2 feet 

 deep to the gravel, and by means of their runs 

 the surface water readily passes down — some- 

 times, indeed, too readily. Under such cir- 

 cumstances, where the mean temperature of 

 the year is about 50°, and the annual amount 

 of rain only 2-1 inches, fruit-trees will fre- 

 quently suffer from dryness at the roots, and 

 therefore ground so situated does not require 

 drainage. Ground lying on a slope with an 

 impervious subsoil, although free from springs, 

 may yet be too wet in certain parts; for where 

 the slope is irregular water may collect in the 

 hollows. But when the subsoil is reduced to 

 a regular slope, and these inequalities removed, 

 the rain-water will not lodge in one place more 

 than in another, and in all probability there 

 will be no necessity for drainage. In short, 

 where the subsoil has, either naturally or arti- 

 ficially, a regular slope, and where no water 

 reaches it, beyond the rain which falls on the 

 area, draining will not be required, except in 

 climates where the average rainfall exceeds 30 

 inches in the year. 



With a uniform, and, it may be, only a slight 

 descent to a lower level, a moderately porous 

 soil, even in a wet climate, may not be in want 

 of artificial drainage; and, on the other hand, 

 ground may be so circumstanced as to be ab- 

 solutely unfit for crops until it be drained, 

 although the depth of the annual rainfall may 

 be comparatively small. Whether, therefore, a 

 soil requires draining or not depends much 

 more upon its nature and other circumstances 

 than upon the quantity of rain which falls on 

 the spot. 



The ground in this country being very irre- 

 gular, the surplus water is conveyed to the 

 ocean by streams and rivers. In some cases 

 these natural channels may require deepening, 

 but in general they can be looked upon as 

 affording sufficient fall for the drainage of the 

 adjoining ground. 



Fig. 803 represents a tract of undulating 

 ground, a large portion of which rests on a 

 porous subsoil, as from B to C, whilst from A 

 to B and c to D are marshy, from the rain 

 which falls on these portions not escaping; and 

 it will be observed that the portion from A to B 

 receives also the water which drains through 

 the subsoil between B and C. 



Occasionally the strata are disposed in the 

 form of a basin, as in fig. 804. The rain which 

 falls at A and B percolates towards the centre, 



Fig. 803. 



and the water may force its way through the 

 thinner part of the mass of clay, as at D; by 

 boring at c an artesian well would be obtained. 



Fig. 804. 



Fig. 805 also represents porous subsoil, in 

 which the water is confined by layers of clay, 

 except when it forces passages, or springs, from 



its pressure, through the upper layer, as at 

 A, B, C. 



In some clay soils a bed of sand or gravel, 

 completely saturated with water, occurs at the 

 depth of a few feet below the surface, with 

 which it has corresponding undulations; but 

 in places where its water is subjected to the 

 greatest pressure, and the stratum of clay 

 above it offers the least resistance, springs from 



Fig. 806. 



it appear at the surface, or it saturates the soil 

 so as to render it only fit for subaquatic vege- 

 tation. Fig. 806 exhibits this arrangement of 

 strata: where A represents the surface soil; 

 B, the impervious clayey subsoil; C, the watery 

 stratum of sandy clay or gravel; D, the lower 

 bed of clay resting upon the rocky strata; E 



