The Scottish Naturalist. I O I 



But it may be asked : If Kinnoull Hill is not an extinct volcano, 

 whence did all the volcanic material come which was poured out over 

 the surface of the land till it had accumulated to the enormous thick- 

 ness of not less than fifteen hundred feet? The supposition proposed 

 by Dr. Geikie seems highly probably that the district was dotted 

 over with a number of low volcanic hills, each of which contributed its 

 quota of lava-streams and ashes. We must also bear in mind the 

 immense antiquity, geologically speaking, of the Kinnoull Hill lavas, 

 and the great changes that have taken place during the geological 

 ages which have elapsed since their formation. 



There appear to have been at least four great periods of activity. 

 The first occurred in Silurian times, and attained its greatest develop- 

 ment in Wales. The next was that of the Old Red Sandstone age ; 

 and is exemplified by the volcanic hills which extend over the greater 

 part of central Scotland, embracing the Sidlaw and Ochill ranges, and 

 with them, of course, Kinnoull and Moncrieffe Hills. The next great 

 outburst occurred in Carboniferous times, when the coal fields were in 

 course of formation. The last period of volcanic activity was the 

 Miocene period. The volcanic product of that period is represented 

 by an immense number of trap-dykes, occurring at various points 

 along the west coast of Scotland. It is probably to that final period 

 of activity that the dyke belongs that forms the most striking 

 example presented by Kinnoull Hill of intrusive volcanic action. 



These different periods show how very ancient, relatively, the 

 Kinnoull lavas are ; and we can now better appreciate the changes 

 that have taken place since their formation. We may take it for 

 granted that the older a volcanic district is, the more of the super- 

 structure of the volcanic products must have been removed ; so that, 

 in a region of very ancient activity, the rocks which are now exposed 

 at the surface are not only more or less altered in character, but 

 represent only the foundation or substructure, as it were, of former 

 volcanic hills ; and it is this foundation that is exposed in Kinnoull 

 Hill. 



