124 THE DEVELOPiVJENT OF BRITISH FORESTEY 



soils it is invariably found that fine soil, either as a thin 

 coating between layers of rock, or in the filling up of the 

 spaces between the larger particles, is always present, and 

 the greater the proportion this soil bears to the unweathered 

 and harder rocks and stones, the better trees grow. While, 

 therefore, the surface layer of ordinary soil is not necessary 

 for trees, tine soil particles must be present within reach of 

 their roots at all times, and in such a condition of fertility 

 as to allow growth to proceed at a normal rate. 



The most favourable timber-producing soils in a general 

 way, and apart from those required for particular species, 

 are deep gravelly loams, porous enough to prevent stagna- 

 tion, and yet containing enough clay in their composition 

 to keep them fresh and moist during seasons of drought. 

 In wet climates little difference probably exists between 

 such soils and those resting on a bed of well broken-up 

 rock which allows the roots to penetrate easily between 

 the fissures. Slates, schists, and thinly bedded sandstones 

 and limestones all produce good timber of most conifers, 

 beech, etc., in the western counties of England, Wales, 

 Scotland, and Ireland, or wherever a summer rainfall of 

 ten to fifteen inches is general. Limestones are possibly 

 more favourable than sandstones to ash and beech, but 

 few other species do so well on them, given equal situa- 

 tions, and depth of surface soils in each case, as on other 

 formations. Lime in the soil equal to more than 1 to 

 2 per cent, of calcium oxide appears to be injurious to 

 Douglas fir and one or two other species. Probably lime- 

 stone formations represent the only geological type, the 

 chemical nature of which exercises any infiuence upon 

 tree growth. On all other formations depth, porosity, and 

 moisture appear chiefly to determine the productive 

 capacity of the soil, assuming, of course, that the latter 

 contains the various elements necessary for maintaining 

 plant growth. 



