CHAPTER IX. 



GEOLOGIC HISTOIRY OF THE VERMILION DISTRICT. 



The earliest period of the history of this district, as of all others, is 

 entu-ely hidden from us. We can go no farther back than the time of the 

 formation of the earliest rocks now exposed to view. Whether during this 

 early time the area of the Vermilion district remained continuously under 

 water after the formation of the primeval ocean, or after an ocea^n existed 

 there was a laud area antedating the development of the oldest rocks now 

 found, can only be conjectured. However this may be, the evidence we 

 now have indicates that this region was for the most part, if not wholly, 

 under water at the time the Ely gi'eenstones were formed. 



The Ely greenstone, as has been shown, consists entii-el}^ of igneous 

 rocks. These are almost wholly lavas and largely of ellipsoidal greenstones 

 which are amygdaloidal and spherulitic, and are therefore presumed to be 

 surface igneous rocks. These greenstones within the district have a great 

 but unknown thickness, and the formation extends far beyond its confines 

 in a continuous belt nearly to Lake Nipigon, Ontario. Furthermore, similar 

 formations occupy equivalent positions in other parts of the Lake Superior 

 region; hence we infer that the time of the deposition of the Ely greenstone 

 was one of regional vulcanism paralleled in magnitude only by the more 

 important later volcanic periods, such as those of the Keweenawan and the 

 Tertiary. 



The length of time involved in the formation of the Ely greenstone 

 can only be conjectured. It is well known that volcanic material accuiuu- 

 lates with great rapidity; hence, so far as the masses of material exposed 

 to \aew may determine our judgment, we would not be justified in con- 

 cluding that this period was one of extraordinary length. However, if we 



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