FLOWERS OF THE ROCKS AND WALLS 



195 



by a great thickness of soil. Indeed, large 

 areas are denuded of soil, forming pavements, 

 and upon these plants grow as upon the slopes 

 where detritus has accumulated. 



The natural type of woodland upon lime- 

 stones is Ash wood, which ranges up to an 

 altitude of 1000 ft. Associated with the .Ash 

 are the W'ych Rim and Hawthorn, the former 

 at lower elevations in damp situations, the 

 latter higher up in dry situations, and either 

 may replace the .Ash locally. 



Juniper and Yew are also found on calcare- 

 ous soils. The Hazel is common, but the 

 .Alder is local. In some areas the Birch is 

 found. Other members of tree or scrub 

 zones are Lime, Buckthorn, Spindle Tree, 

 Scotch Rose, Eglantine, White Beam (as 

 on chalk). Cornel, Wayfaring Tree, Privet, 

 Spurge Laurel. Heaths and Ling are absent. 

 In damp spots the herbaceous types are 

 Marsh ^Iarigold, Meadow-sweet, Water .\vens. 

 Valerian, Butterbur, Melancholy Thistle, 

 Jacob's Ladder, Scorpion Grass, Bur Reed, 

 Reed, &c. 



On dry soils Dog's Mercury and Moschatel 

 are very characteristic types, and in damper 

 places Yellow .Archangel, Ransoms, Bellllower. 

 Ground Ivy, and, where the ground is stony. 

 Hairy St. John's Wort, Nettle, Wood Sage, 

 Lily-of-the-Valley, Melic Grass. 



Rocky knolls occur where there is little or 

 no soil and bare rock, with cryptogams. Sand- 

 wort, Whitlow Grass, Rue-leaved Saxifrage, 

 Biting Stonecrop, Thyme. The woodland 

 ceases where the rocks outcrop, except on the 

 pavements. The screes and cliffs, when damp, 

 are coloniz(;d by the vegetation of the .Ash 

 wood itself. 



Chalk. — Limestone, in the last section, refers 

 to the Pateozoic limestones, which are de- 

 veloped in the molster west and north of Eng- 

 land. The chalk and oolites, also limestones, 

 which are not so compact or altered, are more 

 porous, and, being confined to the southern 

 and eastern parts of the country, are drier, 

 and many of the chalk plants are therefore 

 xerophiles. 



The typical woodland is Beech, but .Ash 

 woods also occur. They occur on the slopes 

 or hangers (a name familar to readers of 

 White's Selborne), growing often on the rock 

 itself, or where the soil is merely a shallow 

 layer of mild humus. With the Beech grow 

 Ash and White Beam, and, locally. Box (as on 

 Boxhill) and Cherry. The Yew is also a char- 

 acteristic tree, native here. In the Beech 

 wood there is little scrub, but on calcareous 

 pastures or the m.argins of the ch.-ilk, White 

 Beam, Cornel, Buckthorn, Wayfaring Tree, 

 Spindle Tree, &c. , are found. 



The scanty ground flora consists of Wood 

 and other Violets, Wild Strawberry, En- 

 chanter's Nightshade, Sanicle, many Orchids, 

 Bird's-foot, Belladonna, Butcher's Broom. 



In addition to Beech, Ash, and Yew woods 

 upon the chalk, there is a scrub association 

 and a chalk pasture. In the last case the soil 

 is often not more than i in. in depth, but an 

 extensive flora occurs upon it, with a turf of 

 .Sheep's Fescue, or, in other cases, of liromus 

 I'Kctiis, Trisctuin /lavescens, Bnxchypudium 

 svhaticum. Occasionally the soil disappears, 

 and here the plants are subjected to intensely 

 dry conditions in a hot summer. 



These gradations of soil thickness, again, 

 show that between rocks pure and simple and 

 rock soils there is very little difference, especi- 

 ally in this case. But where a non-calcareous 

 soil is formed above the chalk, as frequently 

 happens, this is not the case. 



Other Rocks (Maritime). — In addition to in- 

 land rocks and rock soils there are the rocks 

 along the coast, forming cliffs of some height, 

 with bare faces and surfaces covered by grass 

 or heath, &c. The proximity of the sea and 

 the regular occurrence of sea breezes, gales, 

 mists, &c., tend to obliterate the effect of 

 the chemical composition of the rocks them- 

 selves, and to transform the vegetation 

 into a halophytic type of formation. And the 

 conditions upon the cliff face resemble those of 

 mountain-tops, the sides of the cliffs being 

 often spray-covered and moist ; whilst innu- 

 merable caverns exist where moisture-loving 

 ferns are especially at home, and, fortunately 

 for their existence, inaccessible. 



On such rocks (cf. Section VII) occur many 

 maritime species, as Wild Pa;ony (Steep 

 Holmes), Welsh Poppy, Wild Cabbage, Woad 

 (Severn estuary), Sea Stock, Tree Mallow, 

 Scurvy Grass*, Sand Spurrey, Pearlwort, 

 Stonecrop, Samphire, Lovage, Golden Sam- 

 phire, Sea Plantain*, Buckshorn Plantain*, 

 Cotoneaster (Great Ormc's Head, now pro- 

 tected), Thrift*, Sea Lavender, &c. It is a 

 noticeable fact that some of these (marked 

 with an asterisk) occur also upon inland rocks 

 at high altitudes, thus showing the influence 

 of a rupestral habitat. 



Sandy Fields. — In many areas there are 

 tracts of sandy ground, derived from sand- 

 stones or sands, especially in the east and 

 south of England, where the rainfall is small 

 (under 25 in.). Reference has already been 

 made to the probable occurrence of steppe con- 

 ditions in this country following the glacial 

 pha.se. The following pl.ants are found on 

 sandy areas at Mildenhall: Silene Oli/es, S. 

 coiiicn, Holosteitm nmbcUalum (on walls, be- 

 coming rare), Medicaf^o fakata, M. sylvestris, 



