CRYSTALLINE BASEMENT 47 
tural planes of the schist mass. Crosscutting dikes are occassionally 
seen, but more irregular bodies with sinuous contacts and numerous 
-apophyses are not met with. Brecciation, melting and assimilation 
hs are also odd phenomena, except a certain class of banding, 
Fk where a lateral assimilation on a very reduced scale has suc- 
j ceeded. The whole appearance of the intrusion depended appa- 
— tently upon a lateral controlling pressure, causing the mentioned 
i parallel injections along the planes of weakness. The areal exten- 
sion of the resulting banded rocks is a very considerable one. Alt- 
hough they are of the same origin as many common parallel ar- 
: terites in archaean terranes, the banding in the Umango area shows 
a somewhat different character, due to an already mentioned lateral 
a assimilation along the granite veins. The lateral assimilation is com- 
mon especially where the granite intrudes amphibolite schists, from 
which results a product of intermediary composition. This last is 
_ also banded, evidently a result of parallel movements under stress 
conditions. Also at the borders of other schists such a banding 
_ was produced. 
The banding phenomenon has been studied already long time ago 
_ in different archaean terranes. The following two classes may be 
4 distinguished: 1) Banding produced by flowing in a primary magma 
_ with the formation of „Schlieren“ or streaks of different composition. 
: The well known banded gabbro of Skye, Scotland, described by 
Geikie and Teall! belongs to this type. 2) Banding produced by 
_ the injection of magma along the structural planes of a schist mass. 
_ This type is the more important one and is of regional extension, 
as is shown by investigations in many parts of the world.” 
1A. Geikie and J. J. H. Teall: Banded Igneous Rocks of Skye. Quarterly 
_ Journal of the Geological Society of London. Vol. L. 1894. 
| 2J. J. Sederholm: Om granit och gneis. Bull. Comm. Géol. de Finlande. 
| N:o 23. Helsingfors 1907. 
P. J. Holmquist: Zur Petrographie und Geologie von Ornö Hufvud. Bull. 
Geol. Inst. of Upsala. Vol. X. 1910. 
Adams and Barlow: Geol. of the Haliburton and Bancroft Areas, pro- 
