The warmest and driest sites are on sandy and gravelly soil, the coldest and wettest on clay. Chalk is cold but not necessarily damp.

Soil has to be considered not only in reference to climatic conditions, but also in relation to water supply, the character of which in most cases it determines.

In new neighbourhoods the house may be found to stand on " made ground," the worst of all soils, and invariably unhealthy.

The surface soil is not always closely related to the subsoil, and as the latter is often the more important factor in determining the healthiness of the site, it is well to ascertain its nature before deciding to live upon it. Gravel overlying clay, if of no great depth, would imply a wet and cold site, as the surface soil would always be water-logged.