The nature and condition of the soil upon which houses are to be built should receive far more attention than is usually bestowed upon such subjects. A soil which is spongy and damp, or contains much loose organic matter, is generally unhealthy; whereas a dry, porus soil affords a healthy site for buildings. Wherever we find a soil deficient in gravel or sand, or where gravel and sand-beds are underlaid with clay, there should be a thorough sub-soil drainage, because the clay retains the water, and a house built in such a spot would otherwise always be damp and unhealthy.

When the sub-soil is swampy, which is the case with many portions of various cities that have been filled in with what is called made earth, fever is liable to prevail in houses built in such localities, owing to the decay of organic matter underneath, and its ascension in the form of gas through the soil. When good drainage cannot be effected in such situations, and it is found necessary to build houses on them, they should all have solid floors of concrete, laid from the outside of the foundations and covering the whole area over which the structure is erected. These floors tend to prevent dampness in houses, consequently they are more comfortable and healthy than they otherwise would be. Such floors also tend to prevent the cracking of the walls, owing to the solidity and firmness imparted to their foundations.