ROCKS OF THE VERMILION SERIES. 367 



the schist takes a great accession of feldspar and becomes a gneiss. This is 

 also conglomeratic, and in some places is almost entirely composed of bowlders. 

 The formation finally grows silicious and then diabasic, rising in ridges 150 

 feet above the lake. This varying conglomerate is two miles in width across 

 the strike. 



The same observer has noted similar facts on the south shore of Rainy lake : 



" In the southwest quarter of section 30, township 71-22, the mica schist is con- 

 glomeratic, containing innumerable flattened pebbles and bowlders, all changed into 

 rock very similar to the schist. * * * A little farther east the rock assumes the 

 appearance of a decided conglomerate, containing pebbles of granite, quartzite, and 

 schist as large as eight inches in diameter." * 



Generally, however, the Vermilion series is represented by mica schists. 

 These are most frequently biotite schists, or biotite-muscovite schists, or bio- 

 tite-hornblende schists. Transitions from one to the other are of common 

 occurrence. Other characters of these schists are quite ordinary and do 

 uot require mention in a condensed sketch. 



Structural Relations of the Granitoid, Gneissoid, and Schistoid 



Rocks. 



The phenomena observed under this head are extremely interesting. The 

 crystalline schists approach the gneisses under a steep inclination, very gen- 

 erally in Minnesota approximating to verticality. But we never observe an 

 abrupt junction between them. They are always in strict structural con- 

 formity. In thousands of observations on the nature of their approxima- 

 tion I have never seen an undoubted discordance of bedding. There are 

 no such facts in the Northwest as have been pictured in some of the text- 

 books. But all this is not adequate proof of the absence of a chronological 

 break. In fact, the reality of such a break is revealed in the phenomena 

 which I am about to describe. 



In passing from the interior toward the periphery of one of the granitoid 

 areas we find portions of the neighboring schists included within the mass 

 of the gneiss. These increase in amount as we proceed. At an indetermi- 

 nate zone the volume of schist equals that of the gneiss. Then we encounter 

 fragments of the gneiss included in the schist. The schist, meantime, be- 

 comes extremely cut by ramifying sheets of gneiss, granite, or granulite 

 proceeding from the centre. Sometimes a very intricate net-work results. 

 At remoter points these ramifications diminish and the schist finally presents 

 itself in its normal and usual condition. 



The portions of schist are generally angular and flattened. They are evi- 

 dently fragments of schistic sheets separated from the body of the schists 



* Sixteenth Minn. Rep., p. 416. Such expressions as 71-72, above, refer to township and range. 



