The Scottish Naturalist. 197 



the history to be eventually compiled through the labours of this 

 Union, will, as I believe, track the sources of our existing flora and 

 fauna and the various stages in their immigration, and will show 

 what effect the later geological changes had in determining the ex- 

 isting geographical distribution of species. The area embraced by 

 the Union is wide enough surely to allow of these, and other im- 

 portant matters, being worked out in detail. In this connection 

 it has appeared to me, that I might on this occasion indicate cer- 

 tain lines of research, which from a geological point of view, seem 

 to promise no little aid to botanists and zoologists, in their endeav- 

 ours to read the history of our flora and fauna. I am not going 

 to inflict upon you any account of the geology of the East of Scot- 

 land. It is too long a story, and is one of those tales which will 

 not bear much compression. Nevertheless, it is necessary to refer 

 to some of the leading geological features of the district, for the 

 purpose of impressing upon naturalists certain facts which they 

 cannot well ignore if they wish to tell us all that we should like to 

 know about the geographical distribution of our plants and ani- 

 mals. When one looks at the area under the supervision of this 

 Union, one must be struck with the notable variety of its outline 

 or surface-configuration. In the north and west it embraces a large 

 portion of the Highlands ; in the south and south-east it includes 

 a most typical region of the Lowlands. A rapid glance at the 

 geological structure of these districts, would show us that the 

 Highland area is composed for the most part of hard crystalline 

 and sub-crystalline rocks ; while the rocks most abundantly met 

 with in the Lowlands are sandstone and shales. Again, we should 

 find that the isolated hills and belts of high ground which diversify 

 the surface of the latter area, consist chiefly of crystalline rocks. 

 Now, those crystalline and fragmental rocks of the Highland and 

 Lowland districts are of very diverse composition, some being 

 composed largely of silicates of the alkalies and alkaline earths, 

 while others consist chiefly of silica or of clay, or of admixtures of 

 these and other mineralogical constituents. Only in a few places 

 does carbonate of lime form any considerable rock-masses. 



As everyone knows, the soils of a country are composed of 

 disintegrated and altered rock-materials mixed with some propor- 

 tion of organic matter. Under the action of frost, rain, and 

 decaying organic matter rocks are broken up, and their mineral 

 constituents more or less chemically altered ; so that the character 



