This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
A very few simple observations will enable the pupil to discover that meadows differ very greatly in the relative water content. It will be seen very readily that the influence of a cold clay soil is to make some meadows wet or even waterlogged. In other cases the soil may be found to be very dry, and at certain seasons of the year to exhibit a parched appearance, especially in seasons of drought. This would naturally be connected with the existence of a sandy soil. A few rough examinations of soil may with advantage be undertaken to elicit these facts. But the appearance of a cracked surface in summer will very quickly suggest the fact that the soil is a clay.
As a rule, too, the contour of the surface will mould itself according to the distribution of wet and dry meadows, and a connection will be observed between the occurrence of hollows where water will usually lie, and hilly or slightly rounded surfaces where it will run off. So that the difference between soils and the occurrence of hollows and slopes will suggest the division of meadows into wet and dry meadows. Then the plants that are respectively found in each will readily be recognized after a little practice. The occurrence of Clovers and Sandworts, or such very dry soil plants as Mouse-ear Hawkweed, which also grows on walls, will indicate dry soils. The extensive patches of Sedges, Rushes, and Spike Rushes which are found in wet spots will indicate on the other hand wet meadows.