part 1] AXXIVEESART ADDRESS OF THE PRESIDENT. Ixxi 



oldest rocks can be seen, and much study of that difficult region has 

 left some fundamental questions still unsettled. It is not yet a 

 matter of common agreement whether the ' Older ' Grabbros and 

 Granites of the South-Eastern Highlands belong to the same 

 epoch as the Lewisian of the North- West, or to a distinct and much 

 later epoch. 



Leaving this question and others for future solution, we may note 

 meanwhile some very instructive features of these ancient plutonic 

 intrusions. The rocks are of calcic facies, like all other rocks 

 intruded in close connexion with powerful lateral thinist. In this 

 case the connexion is of the closest possible kind. In the South- 

 Eastern Highlands especially it is clearly seen that the earliest 

 inti'usions of magma preceded the clunax of the disturbance, so that 

 the basic members of this rock-series met the brunt as rocks already 

 solid ; while the later and more acid magmas were intruded near 

 the height of the mechanical disturbance, and during its decline. 

 The further circumstance that the region was long maintained at a 

 high temperature had an interesting consequence ; for the stmining- 

 off process, which I have pictured as taking place in the deeper 

 crust, was here effected at a level which is now exposed to view. 

 How in this way broad fringes of pegmatite have been squeezed out 

 from the half- consolidated gi-anites has been well described by 

 Mr. G-eorge BaiTow. The pegmatites are often rich in microcline 

 and muscovite, but this is the limit of their approach towards the 

 alkaline pole. It is instructive to compare these Scottish Archsean 

 granites with those which build the gi-eat Lam*entian batholites of 

 Lower Canada, intruded under very different mechanical conditions. 

 There we find a fringe of albite-gi-anite, albite-syenite, and finally 

 nej)heline-syenite and ijolite. The close s^^nchronism of the British 

 Archaean inti'usions mth powerful lateral thrust finds a parallel, 

 however, in many other parts of the world, and the fact is of prime 

 imjDortance in relation to the crystalline schists. The older sedi- 

 ments were recrystallized under the influence of great stress as well 

 as high temperature, a conjunction not realized on the same exten- 

 sive scale at an}" subsequent period. 



What has been remarked of the ' Older ' plutonic intrusions of the 

 South-Eastern Highlands seems to be true also in the main of the 

 Lewisian series, assigned on the view most widely held to an earlier 

 epoch, and so to an earlier system of crust-movement. Erosion, 

 however, has exposed lower levels in the North- West, and thus has 

 presented us with a different aspect of the igneous economy. In 



