198 The Scottish Naturalist. 



of a soil is necessarily determined by that of the rocks from which 

 it has been derived. Hence, as we pass across a country from one 

 geological formation to another, we find that the soils take on a differ- 

 ent character with every change in the distribution of the underlying 

 rocks. Speaking generally, the rocks in the East of Scotland are 

 disposed in narrow and broad belts, which extend from south-west 

 to north-east ; so that when we traverse the land from north-west 

 to south-east, or across the strike, we encounter a greater variety 

 of soils than we do when the same area is crossed at right angles to 

 that direction, namely from south-west to north-east. But although 

 a south-west and north-east trend is common to all the strata in 

 the East of Scotland, there are yet certain rock-masses which are 

 very irregular in the mode of their occurrence. This is the case, 

 for example, with the granites of Aberdeen and Forfar, and, to a 

 less extent, with many of the igneous rocks of the Lowland area 

 particularly with those of Fife. More than this, we find that the 

 distribution of the soils does not always follow precisely that of the 

 underlying rocks. In every stream and river-course for example, 

 disintegrated material is swept from higher to lower levels, so that 

 the soil of a valley-bottom may differ very considerably from that 

 which the underlying rocks would have supplied. Again, rain is 

 continually washing down soil from the steeper slopes of the land, 

 and hence soils derived from the decomposition of one set of 

 rocks may come to overlie rocks of a totally different kind. In 

 short, it cannot be too constantly kept in mind that all soil is 

 constantly travelling from higher to lower levels. Now this 

 travelling of the soil, which we see taking place before our eyes, 

 was effected occasionally in a very wholesale fashion during former 

 geological periods : with the result that the influence of the 

 underlying solid rocks upon the composition of the overlying soils 

 has often been obscured, or even entirely set aside. During the 

 Ice-age the whole of the area under review was subjected to the 

 long-continued action of glacial erosion. Before the advent of those 

 sterile conditions, the soils and sub-soils of our country must have 

 attained a great thickness. For unnumbered aeons the rocks had 

 been subjected to the influence of the weather — to the mechanical 

 and chemical action of rain and frost, and doubtless, to the action 

 of the organic forces also. Hence long before the Ice-age arrived, 

 our hills and valleys must have been thickly clothed with the 

 ruins of rocks, just as is the case in our own day with those 



