200 The Scottish Naturalist. 



yet cannot be expected to leave nothing for local observers to 

 accomplish. From the maps of the Survey we shall get the 

 general geological structure, the direction of glaciation, and the 

 distribution of superficial deposits. With these data for a ground- 

 work, it should not be difficult for the local observers in each 

 Society of the Union to construct correct soil-maps of their re- 

 spective districts. Were this accomplished for the East of Scot- 

 land, we should soon be able to ascertain to what extent geological 

 structure influences the distribution of species. 



It goes without saying, however, that soil is not the only factor 

 which naturalists have to take into account. Every farmer knows 

 that good soil is of little avail if it be not favourably placed. The 

 same soil under diverse conditions may support very different floras. 

 The physical features of the surface, therefore, have to be noted ; 

 the relative height above the sea, rainfall, temperature, and all that 

 comes under climatic conditions, must likewise be considered. Very 

 slight differences sometimes give rise to strong contrasts in the flora 

 of a district. Thus I have frequently observed in hilly districts, 

 where all the conditions of soil and drainage were similar over a 

 wide region, that those slopes which faced the direction of the 

 rainy winds were clothed with the densest and thickest turf or peat. 

 This is strikingly marked in the case of the peat-covered hills of 

 western Galloway, where, on the slopes looking westward, the peat- 

 bogs are fresh and growing ; while on the eastward slopes they are 

 often dried up, and in many cases are being gradually disintegrated 

 and denuded away. Naturally, then, we shall expect to find that 

 climatic conditions everywhere modify the influence of the soil in 

 the distribution of species. 



I have suggested to the geologists of the Union the construction 

 of soil-maps of the district. It would be a great matter to obtain 

 rough analyses of the various typical soils. This might often be 

 done by the geologists themselves. Let them select their speci- 

 mens from the bottom of the soil-bed and the upper portion of the 

 subsoil. By carefully washing and sifting, they will soon take out 

 the microscopic or coarser ingredients, the nature of which will 

 readily be determined by the eye or with the aid of a lens. The 

 finer residue could then be examined under the microscope, and 

 some simple chemical tests would soon detect any matter that 

 remained in solution. Very often a microscopic inspection alone 

 would suffice to show the general composition of a soil. If, for 



