4. _Springs and Wells._—Attend to the quality and quantity of the water; whether it will serve for the cavalry, as well as infantry, and the manner of its being drawn. Observe the situation of the spring, and of its source, whether it can be protected, and the enemy prevented from cutting it off. 5. _Lakes, Marshes, and Swamps._—Learn their cause; if arising from a moist soil, the overflowings of rivers or from springs. Observe their situation, and the appearance of the surrounding country; the best means of crossing them. If they are divided by causeways, notice their breadth and condition; if not, remark if causeways can be easily established, and whether the swamp can be drained, and whether it is passable at any season of the year. Observe the points from which the causeways can be defended against the passage of an enemy’s column. Learn whether or not the swamps are subject to fogs; and at what seasons they are most hurtful. 6. _Of Woods and Forests._—Remark their extent; their situation; their thickness; whether the trees are lofty or low; whether there is much underwood. Observe if the different clumps form openings or passes; and their extent; whether their sides are formed of thick wood or brush; whether their breadth is uniform, or widens at particular parts. Remark whether the ground of the forest be level or hilly, swampy or dry. Observe the nature and condition of the roads (for remarks to be made on these, see the article _Roads_;) observe also the means the forest affords of intrenching; of making fascines, abbatis, &c. Attend to the face of the country round the forest, whether cultivated fields or meadows: whether it affords positions; is intersected by rivulets, swamps or ravines. Remark the castles, villages, towns, &c. in the neighbourhood; and their distance from the skirts of the wood. Go round the wood and examine its principal débouchés; observe the ravines, rivulets, roads, &c. issuing from it, and learn their direction. 7. _Heaths._—Notice for what nature of troops they are best calculated. The nature of hedges and brush wood; some form a good breast work. Observe the directions of the rivulets, roads, and ravines. When the ground of a heath is of the common colour, the roads are usually good: but when it is blackish and mixed with white sand, the roads are generally impassable in winter seasons. 8. _Canals._—For this article see also the observations on _Rivers_. Observe their intention; the nature of the soil in which they are dug, their breadth and depth; their locks; the craft found upon them; the best means of protecting or destroying them: learn the countries they pass through.