Peaty soils: Peat soils are found in areas which have been waterlogged over a long time so that dead vegetation has been unable to rot down properly with the aid of aerobic bacteria. Very peaty soils are extremely acid and light in texture, drying out and even blowing away in dry, windy weather. Most ericaceous plants and many other calcifuges (lime-haters) will only grow well in such conditions, but others need a more alkaline soil to give the best results. You can add lime to increase the pH, and a method of stabilizing the texture to make it less fly-away is to deep dig to bring up and incorporate some of the subsoil. Many peaty soils overlie clay (this is why they tended to be waterlogged a long time ago), and in such a case this method of soil improvement can be quite successful, but you really have to know what you are doing, as any other subsoil is quite often absolute rubbish as far as the grower is concerned. In any case, often the subsoil is so far below the surface as to make this a totally impossible job for the amateur, so it is possibly better to grin and bear it as most plants will grow perfectly well in a peaty soil, properly managed.
Chalk: This is a thin, dry hungry soil formed from the impurities in an area covered by calcium carbonate (which has been washed away by carbon dioxide from the air dissolved in rainwater). It is not an easy soil to grow plants in, but can be considerably improved by the regular addition of humus-forming material.
Marl: This is a mixture of clay and chalk which on its own is quite difficult to cultivate, but can be improved by increasing the amount of humus in it. It is sometimes possible to obtain marl by the load which can be used as a top dressing for peaty or sandy soils — the chalk increases the alkalinity and the clay gives the soil body.
Stony soils: These are soils containing a disproportionate amount of various sizes of stones. They are usually quite manageable, but the stones tend to work their way to the top and look unsightly, and they can be frustrating to dig because the blades or tines hit the stones. Also they have to be raked off a seedbed or the seeds will not come up evenly. You must pick them off a newly seeded lawn or they will damage the mower. Some very stony soils tend to be rather thin and impoverished, but can be improved as described for chalky soils.
Soil colour: The colour of a soil plays a large part in how well it performs. The colour partly depends on the original colour of the rocks it is formed from, especially those containing iron, and partly on the amount of humus it contains, which tends to make it darker.
Dark soils are preferable to light-coloured ones, as they absorb more of the suns heat and warm up quicker in spring. Although the colour of a soil is largely a thing you are stuck with, a light-coloured soil can be darkened to a large extent by increasing the amount of humus it contains, which can only be good for it in every respect, or by adding weathered soot.