Again, how often a farmer is troubled with a pond or a patch of marshy ground right in the midst of his fields. It is of no use, and simply serves to make the field in which it occurs more difficult to plough and to cultivate--besides being so much good land wasted. Now the reason for the existence of that pond or marsh is that underneath the surface there is an impervious layer in which, as in a basin, the water can collect. Make a hole in that and it will no more hold water than a cracked jug will. And to make that hole with dynamite is the easiest thing in the world. If the pond be merely a collection of water which occurs in wet weather, but which dries up quickly, there simply needs to be drilled a deep hole and a fairly strong explosion caused at the bottom of it. How deep the hole must be depends upon the formation of the earth at that point, and how low down is the stratum which, being waterproof, causes the water to remain. It is that, of course, which must be broken through, and so the explosion must be caused at a point near the under side of that layer. With a little experience the operator can judge the position by the feel of the tool with which he makes the hole. If the pond is permanent but shallow, men can wade to about the centre, there to drill a hole and fire a shot. If it be permanent and deep, then the work must be done from a raft, which, however, can be easily constructed for the purpose. Once broken through, the water will quickly pass away below the impervious stratum and useless land will become valuable. The same may be done on a larger scale by blasting ditches with dynamite. This is in many cases much cheaper than digging them. A row of holes is put down, or even two or three rows, according to the width of the proposed ditch. In depth they are made a little less than the depth of the ditch that is to be. And for a reason which will be apparent they are put very close together, say three feet or so apart. Preparations may thus be made for blasting a ditch hundreds of feet long and then all are fired together. The earth is thrown up by a mighty upheaval, a ditch being produced of remarkable regularity considering the means by which it is made. The sides, of course, take a nice slope, the debris is thrown away on both sides and spread to a considerable distance, so that, given favourable conditions and a well-arranged explosion, there is constructed a finished ditch which hardly needs touching with spade or other tool.