CHERT FORMATIONS OF NOTRE DAME BAY 593 



of iron-rich bands and pure silica, and the outlines of the grains of 

 quartz of which the rock is now composed are entirely independent 

 of this banding. Also, segregation of iron oxide into aggregates of 

 hematite plates, the aggregate bordered by clear silica, must have 

 taken place when the silica was in a gelatinous condition. The 

 occasional occurrence of radiating chalcedony about these aggregates 

 supports this view. 



In connection with the concentric structures referred to above 

 may be mentioned again the botryoidal upper surfaces of some 

 Ordovician cherts of southern Scotland (p. 589). 



Source of the Solutions 



Since the conditions under which the cherts of Notre Dame Bay 

 were formed are beheved to be much the same as those under which 

 some of the iron-bearing formations of the Lake Superior district 

 were formed, it is of interest to examine the views of the workers 

 in this field as to the source of the solutions. Van Hise and Leith^ 

 consider two sources of solutions which would produce a chemical 

 precipitate. The first is a direct emanation from a submarine 

 effusive. This emanation they believe to have carried a ferrous 

 iron salt, probably the sulphate, and siHcates of the alkaHes. The 

 second source of the active solutions is the reaction of the molten 

 rock with sea water, and experiments were conducted to test the 

 efficacy of this process. "Fresh basalts were heated in a muffle 

 furnace to a temperature of 1,200° C, a temperature sufficient to 

 fuse the exterior, and then plunged into salt water of the composition 

 of sea water, the result being a violent reaction, producing princi- 

 pally sodium silicate but also bringing a small amount of iron into 

 solution."^ 



The work of Dewey and Fleet^ has an important bearing on this 

 subject. They describe the pillow lavas of Cornwall and Devon. 

 A peculiar feature of these rocks is that their feldspars have been 

 extensively altered to albite, and it is shown that this took place 



' C. R. Van Hise and C. K. Leith, "Geology of the Lake Superior Region," Mon. 

 N(T. 52, U.S. Geol. Survey. 



^ Ibid., p. 516. 



3 H. Dewey and J. S. Fleet, "On Some British Pillow-Lavas and the Rocks Associ- 

 ated with Them," Geol. Mag., New Ser., Decade V, Vol. VIII, pp. 202-9 and 241-48. 



