The type of rock termed siliceous is characterized by the closeness of the texture, as opposed to the openness and porosity of sandstones. The rock is denser, in fact, and when wet is pasty. Though plants do not favour bare rock surfaces, yet some are to be found upon siliceous rocks where there is but little soil formed, or nothing but detritus, and in the clefts of siliceous rocks some crevice plants do grow, such as the Rowan Tree, Holly, Ash, Birch, Oak, and occasionally even Willow.

Many shrubs, especially Brambles, Roses, Hawthorn, Hazel, may be found growing also on siliceous rocks in damp situations, as around slate pits or natural exposures. Of other types may be mentioned such plants in the ground vegetation as Columbine, Carda-mine impatiens, which I have observed on talus slopes of older Palaeozoic rocks in Shropshire, Bush Vetch, Wild Strawberry, Enchanter's Nightshade, Woodruff, Wall Lettuce, Wood Loosestrife, Epipactis latifolia, Luzula maxima, Carex pendula, and many ferns in the clefts.

Where the conditions are drier, Heath Bed-straw, Mouse-ear Hawkweed, Foxglove, Wood Sage, Sheep's Sorrel, Bluebell, etc., are found. Navelwort, Orpine, grow as crevice plants, and so does Golden Rod, and on slopes with little soil Field Mouse-ear (the latter also on marlstone).

Sandstones.1 - Siliceous soils are fine-grained, whereas sands and sandstones are much coarser and looser, more porous. They are consequently drier than the former. Very little humus is formed upon them, and the soil is deficient in mineral salts as a rule. Such soils are characterized by woodland and heath formations. The woodland is dominated by the Oak, both pedunculate and sessile types. The occurrence of Rowan and Birch is characteristic, and also of Bluebell, Bracken, Yorkshire Fog, Tormentil, Foxglove, etc. This is the typical succession where a sandy soil is developed, but frequently such areas may exhibit the rocks themselves in natural exposures, and some plants may be found to grow on the all but bare surfaces, or in crevices, as Orpine, Golden Rod, Sheep's Sorrel. Where flowering plants do not colonize such bare rocks, cryptogams are abundant.