GRAVEL. 



131 



GREENHOUSE. 



dened individually in a loose state ; 

 and even if rolled afterwards, they 

 will never become quite firm. It 

 must also be observed, that large and 

 small stones do not bind well toge- 

 ther ; and hence all gravel, as soon as 

 it is taken from the pit, should be 

 sifted through a wire screen, the 

 wires of which are only sufficiently 

 wide apart to admit stones of the size 

 of a moderately large gooseberry, and 

 all the larger stones should be thrown 

 on one side to be broken. The gravel 

 that has passed through the screen 

 should then be examined, and if it 

 be found mixed with too much earthy 

 matter, it should be again sifted 

 through a wire sieve, sufficiently fine 

 to allow only the earth to pass 

 through. Part of the earthy matter 

 should then be well mixed with the 

 gravel and broken stones, in the pro- 

 portion of one third of each, and the 

 whole should be laid evenly on the 

 walk, and rolled immediately. 



When gravel walks have become 

 loose from time or frequent sweeping, 

 or from the gravel being originally of 

 a bad quality, they may be rendered 

 firm by forking them over; and, after 

 raking out the largest of the stones, 

 and breaking them, mixing the gravel 

 with equal parts of sand and ferrugi- 

 nous clay in a somewhat moist state ; 

 rolling the whole as soon as the ma- 

 terials have been equally spread over 

 the walk. If, however, neither sand, 

 nor ferruginous clay can be easily pro- 

 cured, burnt common clay powdered 

 may be mixed with the gravel ; the 

 clay having been burnt by spreading it 

 on the furnace of a hothouse, or by 

 mixing it with faggots, and then set- 

 ting fire to the whole ; but in this 

 case also, care must be taken that the 

 mixed clay and gravel are watered 

 after they are laid down, and imme- 

 diately after rolled. 



There are various substitutes for 

 gravel. Where colour is- the object, 



as well as firmness and smoothness, 

 there is nothing better than burnt 

 lumps of clay, reduced to a very 

 coarse powder, and slightly mixed 

 with Roman cement. Where colour 

 can be dispensed with, a most effective 

 garden-walk, and one which will last 

 for many years, may be formed of the 

 scrapings of public roads, which have 

 been made, or metalled , as road-makers 

 term it, with granite, or other coarse 

 stone, mixed with tar, laid down to 

 the depth of six inches on a bottom of 

 broken stone, and smoothly and firmly 

 rolled. The different kinds of asphalte 

 so laid down also make smooth and 

 durable walks ; but they are too ex- 

 pensive for general use. Where no 

 gravel can be procured, granite or 

 other stone, broken very small, and 

 firmly rolled, will make a very dura- 

 ble walk, though the colour is far 

 inferior to that of fine yellow gravel. 

 For laying out walks, and the mode 

 of preparing the foundation of gravel 

 walks, &c, see Walks. 



Greek Valerian. — See Pole- 



MONIUM. 



Greenhouse. — A structure for 

 growing those plants in (more parti- 

 cularly in the winter season), which 

 will not endure the open air of British 

 winters. It may be of any form, but 

 the most convenient is a square or a 

 parallelogram, with upright glass in 

 front, sufficiently high to admit of 

 walking upright under it immediately 

 within the glass ; and with a sloping 

 roof, at such an angle as readily to 

 throw off the rain. This roof, for 

 the better receiving the sun's rays, 

 should face the south, south-east, or 

 south-west, and this is called the 

 aspect. The front should seldom be 

 lower than seven feet in height, and 

 the height of the back should be about 

 two-thirds of the width of the house. 

 The space within is generally laid out 

 so as to have a shelf in front, about 

 two feet high from the ground, and 

 k2 



