The Scottish Naturalist. 199 



land surfaces that have never experienced glaciation. All this 

 loose material was swept forward under the ice-sheet which 

 mantled Scotland ; and the solid rocks themselves were bared, 

 abraded, and quarried by the ice. When the ice melted away, its 

 ground-moraine was left sprinkled over hill-tops and slopes, and 

 spread in more or less continuous sheets over the low-lying and 

 gently undulating regions. Thus wide areas of solid rock are 

 now and again buried under great depths of materials which are 

 more or less, foreign to the district in which they occur. The 

 debris of the Highland region, for example, is thickly spread in 

 Strathmore, while material derived from the degradation of the 

 rocks of Strathmore is met with all over the area of the Sidlaw 

 Hills. Thus, throughout wide tracts in East Scotland the vege- 

 table soils are not derived directly from the disintegration and 

 decomposition of the underlying solid rocks, but from the weather- 

 ing of ancient morainic and fluvio-glacial accumulations, much of 

 which consists of travelled material. Hence we may expect to 

 meet with very different kinds of soil distributed over the surface 

 of one and the same geological formation. I think it is partly 

 because of this that naturalists have somewhat undervalued the 

 influence of geological structure upon the distribution of our flora 

 and fauna. They look at a geological map, and see broad belts 

 of mica-schist, or slate, or sandstone, or igneous rock, as the case 

 may be, represented as extending for great distances, and yet 

 these variously coloured bands of rock do not seem to correspond 

 to any relative changes in the distribution of plants and animals. 

 But a very cursory examination of the subsoils will show that 

 these are frequently made up to a large extent of material derived 

 from some neighbouring district — so that debris from the im- 

 mediately underlying solid rocks may enter but meagrely into the 

 composition of the vegetable soil. When this simple fact is borne 

 in mind, naturalists will hesitate to conclude that geological 

 structure is not one of the factors with which they have to deal. 

 Now it would be a very great aid to botanists and zoologists if 

 they had prepared for their use geological maps which showed not 

 only the distribution of the " solid " rocks, but that of the over- 

 lying superficial accumulations. By-and-by the Geological 

 Surveyors shall have completed their work ; and the maps issued 

 by them will be of great service to local geologists, who will find 

 that however careful and exhaustive a general survey may be, it 



