fuel, and 109 tons net of water were raised, per stroke, to the height of 10 ft. The boilers of the Leeghwater engine are five in number, cylindrical, and each 30 ft. long, and 6 ft. in diameter, with a central fire tube 4 ft. in diameter. Under the boilers a return flue passes to the front, and then divides along the sides. Over the boilers, and communicating with all of them, is a steam chamber, 42 ft. in length, and 4 ft. 6 in. in diameter; from which a steam pipe, 2 ft. in diameter, conveys the steam to the engine. The consumption of fuel is 21⁄2 lbs. of coals per horse power per hour, when working with a net effect equal to the power of 350 horses. The cost of the "Leeghwater" and machinery was 21,000l., and of the buildings and contingencies, 15,000l. It has been calculated that the entire cost of the works for draining the lake will be 100,000l. less than would have been incurred by adopting the ordinary system of steam engines and hydraulic machinery, and 170,0007. less than the expense of applying the system of windmills hitherto prevailing in Dutch drainage. The annual cost of the three methods is thus estimated: by three engines, such as the Leeghwater, 4500l.; by windmills, 61007.; and by ordinary steam-engines, 10,000l.

82. The several methods of draining, as already explained in reference to Figs. 9, 10, and 11, are also more or less applicable for districts of the kind sketched in Fig. 12, and also for the second class or Upper Districts. Thus, the drainage from the high lands have to be received and collected in catch-water drains at the base of the hills, and means taken for combining these waters with those from the level district, or of keeping them separate, as may be required. Or reservoirs may be formed in connection with the catchwater drains, so that irrigation may not be necessarily

suspended in cases of drought or deficiency of rain

water.

83. We have hitherto limited our attention to the disposal of such waters as are naturally supplied to districts of the several characters referred to. But, having included the supply of water as an allied purpose with that of draining, we may briefly notice the means which are commonly available for maintaining this supply, augmenting it when deficient, as well as discharging it when excessive. The expedients for this purpose have to be considered chiefly with reference to the upland districts, some of which are liable (even with all the aid that can be rendered by economy of the natural supply) to suffer from an inadequate command of water. Thus, if, as shown in Fig. 31, the surface of the district A A

Fig. 31.

B

B

D

C

have a stratum of clay or other impervious material, B B, immediately beneath it, the outer stratum will remain always comparatively dry, the rain and drainage waters eagerly flowing downward, while the clay resists their passage into the subsoil. Beneath the resisting layer, however, a permeable and saturated soil, as cc, is often

situated, and in these cases an adit drain at D, or other convenient point, will bring the internal water to the surface, and probably aid the supply of the district with the drainage waters from a higher and overcharged level. Internal springs are also in some cases available for this purpose, and may be brought into use by simple and inexpensive means. If these resources fail, it may become desirable to apply mechanical power for raising the necessary quantity of water from a river or other

reservoir at a lower level.

84. Of the various forms of apparatus which have been devised and applied for the purpose of raising water, it would be nearly impossible to give here even a bare catalogue. Many of them are actuated by the accumulated force of small streams from superior levels; but these are, of course, useless in cases where greater economy is attained by using these upper streams directly upon the surface of the district. Pumping engines, worked by steam or other artificial power, form the only class of machines by which the required accession of water can be brought up from the lower source. If the lower source, however, be a tidal river, the pumps may be worked by an undershot water-wheel placed upon it, and the water be delivered above into an artificial channel or aqueduct, and thence conducted to the higher levels. Apparatus of this kind being, however, more generally applicable for the supply of water to towns than to large districts of land, our notice of it, brief as it must be, will be more appropriately introduced in the Second Division of this work.

SECTION III.

Means of Conveying, Distributing, and Discharging Water.-Drains and Watercourses.-Forms, Sizes, and Methods of Construction.-Implements employed.—Shallow and Deep Draining.—Stone, Tile, and Earthenware Drains, &c.

85. Having in the preceding sections shown the general principles of draining, as applicable according to the general profile of the district, we have now to direct our attention to the details of the system; to show the methods to be selected with reference to the nature of the soil and the position of the substrata, and to consider the arrangement, form, size, and construction of the drains which it may be necessary to provide in order to promote the objects of agriculture.

86. The nature of the several soils which we have to deal with will be best understood by regarding the manner in which they have been formed, and the several materials of which they are constituted. The formation of all soils may be very clearly traced to the disintegration, by mechanical and chemical agencies, of rocks and minerals which contain alkalies and alkaline earths. In the mountainous districts of perpetual snow, the most refractory rocks are crumbled into fragments, which, being rounded by the action of glaciers, or pulverized into dust, are borne down by the rivers and streams, and deposited upon the plains and valleys below. Some of the most remarkable proofs of the influence of the air, water, and carbonic acid upon the constituents of rocks are exhibited in parts of South America, where the elements of the silver ores are gradually dissolved and dissipated by the action of these agents in the winds and rains, and the metal, resisting

the destruction, is left exposed in sharp angular projections from the surface of the rock*.

87. The yellow clay which occurs so frequently in Denmark is considered by Forchammer to have been formed from granite, the felspar of which has undergone change, while the mica has not; the quartz forming the sand of the clay. The blue clays, having no mica, appear to have been formed from sienite and greenstone. The great stratum of clay which occurs at Halle has resulted from the disintegration of porphyry. Most of the sandstones contain silicates with alkaline bases, and in the sandstone of the Holy Mountain, near Heidelberg, fragments of felspar are observed partly changed into clay, and visible at white points in the sandstone. Felspar is unable to resist the solvent action of water when saturated with carbonic acid. Clays formed by the disintegration of felspars containing potash are free from lime; those formed from Labrador spar, which is the principal component of lava and basalt, contain lime and soda. Most rocks, as felspar, basalt, clay slate, porphyry, and the numerous varieties of the limestone formation, consist of compounds of silica with alumina, lime, potash, soda, iron, and protoxide of manganese; and from the fact that most of these ingredients are susceptible of uniting with oxygen, the cause of the disintegration of the rocks which they constitute may be readily and fairly inferred. Of these constituents, the protoxide of iron has a great disposition to absorb oxygen from the atmosphere; thus forming the higher oxide or peroxide of iron. This property is indicated by the reddish brown colour of the rich ferruginous soils, while the black colour of the subsoil shows the presence of the protoxide. In the process of subsoil

Darwin, Liebig, &c.