PRESIDENTIAL ADDRESS. 593 



spilling over from one irregular basin into another. On entering a new district 

 there seems a hopeless confusion of pinkish gneiss and grey-green schist, but 

 presently orderly forms take shape upon the map as the numberless bays and 

 islands are explored, and the ground plan of vanished mountain ranges begins 

 to show itself. Dr. Andrew C. Lawson, in his brilliant study of the Lake-of-the- 

 Woods and Rainy Lake regions in 1884 to 1S88, first brought out distinctly the 

 relationships ; and later work has added greatly to our knowledge of these 

 ancient structures. 



The typical arrangement is that of rounded or oval batholiths of gneiss, or 

 of granite merging at the edges into gneiss, with schists dipping steeply away 

 from them on all sides. Where the batholiths approach one another the green 

 schists occupy narrow troughs between. As shown by Lawson, they are evidently 

 the bottoms of synclines nipped in by the rising areas of granite and gneiss. 

 Round these eruptive masses the schists have a strike parallel to the edge of 

 the gneiss, so that they do not form ordinary synclines, but widen and narrow 

 and swing in curves to adjust themselves to the varying relations of the 

 batholiths. The meshes of green schist are often not complete, the curving ends 

 feathering out to a point. In such places erosion has eaten the surface down 

 below the bottom of the syncline. 



The batholiths in Western Ontario are of all sizes, from a mile to 60 miles 

 or more in diameter, and they are commonly somewhat elongated from west to 

 east or from south-west to north-east. They do not always follow one another 

 in orderly succession, but may lie scattered irregularly, almost like bubbles on 

 foamy water. Yet on the large scale one can recognise a general trend in the 

 direction of the longest axes of the batholiths, and the average strike of the 

 schist in the various regions lies between 50° and 80° east of north, conforming 

 to the same direction. This general east-north-east trend of the basement struc- 

 tures doubtless reveals the axial relations of the Archaean mountain ranges. 



It is sometimes stated that the so-called V formation of North America 

 was made up of two ranges converging toward the south, the easterly arm of 

 the V parallel to the Appalachian mountains and the westerly one to the Rocky 

 Mountains. The structural arrangement just outlined does not confirm this 

 view, but suggests irregularly parallel chains, cutting the direction of the 

 Rockies at about right-angles and that of the Appalachians at an acute angle. 



Of what kind were the mountains erected on these bubble-like foundations of 

 gneiss, set in meshes of schist ? In many places they do not seem to have 

 formed continuous ranges such as those of the Rockies, but rather groups of 

 domes of various sizes. Some of them were comparatively low; others seem to 

 have been lofty, though broad. Of the low ones the best known is that of the 

 Grande Presqu' Isle in the Lake-of-the-Woods, an oval of gneiss IS by 32 miles 

 in dimensions. Here the up-swelling could not have been great, since the schists 

 dip away from the gneiss at low angles all round, and patches of green schist, 

 remnants of the roof, or perhaps of unusually large blocks stoped from above, 

 are fCund here and there in the interior. 



On the other hand, the Rainy Lake batholith, 30 by 50 miles in dimensions, 

 must have risen as a lofty dome, since the surrounding schists dip away at high 

 angles (60° to 90°). The arch of which they were the bases must have swung 

 thousands of feet above the present surface of the batholith. Passing inwards 

 from the Keewatin one finds at first immense slabs of the schist shifted a little 

 and enclosed in gneiss, then bands of green material with softened edges, and 

 finally darker cloudy streaks in the gneiss representing more perfectly digested 

 bands. As Lawson has shown, the outer edge of the batholith is of greyish 

 hornblende syenite gneiss or hornblende granite gneiss, while the interior is of 

 ordinary mica granite gneiss. The outer part has absorbed a certain amount of 

 basic Keewatin material. 



One cannot doubt that this zone of green schist fragments, followed by greyish 

 hornblende rock, originally extended over the dome as well as round its edges. 

 In the middle there is now a width of 10 or 12 miles of the ordinary Lauren- 

 tian gneiss. This implies, of course, that the upper part of the dome, afterwards 

 removed, was several miles in thickness, and that the mountain mass rose 

 correspondingly above the synclinal valleys. It must not be assumed that the 

 dome had a regular surface, nor that it was unbroken. Such a batholith as that 



