Book III. EMBANKMENTS. 717 



cases where the basis is sand, silt, or gravel ; or a mud or black earth, as in some parts of 

 Cambridgeshire and Lincolnshire, which does not easily become so compact. Here it is 

 common, before beginning the bank, to bring up from the solid substratum (<?) what is 

 called a puddle-ditch, or section of clay in the centre of the highest part of the mound in the 

 direction of its length, and of three or five feet wide, according to the depth of the stratum 

 of silt (6), and the intended height of the bank (c). When the clay of this puddle-ditch 

 is well worked, either by men's feet or clay rammers, the bank will be perfectly imper- 

 vious to water, and if against a mild stream or shore, need not contain such an accumu- 

 lation of earth as where the imperviousness of the bank to water depends chiefly on the 

 mass of materials. As already observed, the important point to attend to in this variety 

 of mound is, to found the section, or wall of clay, so deeply as to be in contact with a 

 stratum (a , either by induration, or its argillaceous nature, impervious to water. In 

 the drainage of the Bar Loch in the county of Renfrew, considerable difficulty was expe- 

 rienced in some places in getting to the bottom of the sandy subsoil, so as to bring up the 

 668 puddle wall from the retentive stratum. Such 



~7pp"v^ was the difficulty in some cases, that the puddle 



could not be carried up perpendicularly, but a 

 " ",7-- , puddle wall being raised within the bank, as 

 mW '■■'■ n 'S n as tne natura l surface, it was joined hori- 



■■-■'"'■' ■-"-'■"-v-ii^^'/V": ' .>-"-;-V;"*'--.':'".;'" : -'--. : -; . - ' -, : zontallv to another puddle wall in the bodv of 

 W//Mmf/////////W//7///7/////M t he bank. {fig. 668.) 



4547- Puddling is often found defective, owing to the imperfect working of the materials. Many think 

 that when clay is used, if it be worked into the consistence of dough, it is sufficient ; but this is a mistake : 

 it should be slaked and so decomposed by the labour of proper tools and treading, and so completely satu- 

 rated with water, that the whole mass becomes one uniform and homogeneous body, and almost fluid. 



4348. Mounds with reversed slopes. In some cases of embanking rivers, as where they 

 pass through parks, it is desirable to conceal, as much as possible, the appearance of a 

 bank from the protected grounds. Hence the mound is simply reversed, the steepest 

 side being placed next the water. It is proper to observe, that such banks are not so 

 strong, by the difference of the weight of the triangle of water which would rest on the 

 prolonged slope, were it placed next the river, and are more liable to be deranged in 

 surface in proportion to the difference of the slopes, the water acting for a longer period 

 on every part of the slope. 



4349. Mound faced with stones. This is the same species of mound, with a slope 

 next the water of forty-five or fifty degrees, paved or causewayed with stones or timber. 

 In Holland this pavement or causeway is often formed of planking or bricks ; but in 

 England generally with stones, and the mortar used is either some cement which will 

 set under water, or, what is better, plants of moss firmly rammed between them. The 

 objections to such banks are their expense, and their liability to be undermined invisibly 

 by the admission of the water through crevices, &c. They are, therefore, chiefly used where 

 there is little room, or where it is desirable to narrow and deepen the course of a river. 



4350. The bank formed with piles, brushwood, and stones, is occasionally used for pro- 

 tecting moving sands, or directing the course of streams flowing through a sandy shore. A 

 dike or bank for the latter purpose {fig. 669.) has been erected on theriver Don in Aberdeen- 



g69 shire. It consists of piles or poles, 



being the thinnings of plantation 

 jl of Scotch pine and larch, driven six 

 feet into the sand (a a a) : the 

 spaces between these piles (b b) are 

 tilled in with furze or other spray 

 ' or small branches ; and on the top 

 of them, are wedged in stones to 

 keep them down. On the side of this row of piles next the river, stones (c) from 

 50lbs. to half a ton weight each, are precipitated from a punt, until they form a bank of 

 an angle of nearly 45°. On the outside of this bank and piles, the sand (d) gradually 

 drifts up, and forms a bank, which, being planted with ^rundo arenaria and other grasses, 

 gradually becomes covered with verdure. (High/and Soc. Trans, vol. vii. p. 91.) 



4351. Mound protected by a icicker hedge. This is a Dutch practice, and, where 

 appearance is no object, has the advantage of not requiring watching. \\ icker-work, 

 however, subjected to the strain of waves, will be obviously less durable, than where 

 it lies flat on the ground, and can only decay chemically. This wicker hedge is some- 

 times a series of hurdles supported by posts and studs ; but generally in Britain it is a 

 dead hedge or row of stakes, wattled or wrought with bushes presenting their spray to 

 the sea or river. Besides placing such a hedge before a bank, others are sometimes 

 placed in parallel rows on its surface ; the object of which is to entrap sand, shells, and 

 sea weeds, to increase the mass of mound, or to collect shells for the purpose of carrying 

 away as manure. 



,; A Y 



