

THE VERMILION LAKE PLATE, 1899. N. H. WINCH ELL. 



sedimentary rock, becoming siliceous slates and siliceous argillyte. The latter is 

 curled and banded like a fluidal molten rock, but it is not, so far as known, associated 

 with structural alternations of green schist or other clastic materials. This is sup- 

 posed to have been originally a basic obsidian, quite like the obsidians of the Mesabi 

 range, ejected in submarine conditions.* The effect of such igneous action on the 

 ocean was the chemical precipitation of silica and iron. Such precipitated silica not 

 only permeated and replaced the most of the noncrystalline matter of the obsidian, 

 but, when abundant and continued long enough, it formed sedimentary, banded 

 jaspilyte. These two are not to be confounded with the fragmental secondary jaspi- 

 lyte above referred to as belonging to the bottom of the Upper Keewatin. The iron 

 itself was also probably chemically precipitated by the ocean, in part, and was derived 

 in part from the alteration of the basic glass. * Occasionally a taconitic sand, at least 

 the taconitic structure, has been found in connection with the jaspilyte of the Ver- 

 milion range, indicating the Lower Keewatin accumulation of obsidian sands in the 

 vicinity of obsidian ejection in a manner similar to that already described along the 

 Mesabi range. N. H. w. 



"This distinction was not made in the chapter devoted to this plate in volume iv, tut was included in the descriptions in 

 volume v. 



