GEOLOGY OF THE NORTHWEST OF LAKE SUPERIOR. 223 



Kamanistiquia Rivers on one side, and the Pigeon River on the other — 

 for 50 or 75 miles inland. Near the Current River, the chloritic 

 slates of the eastern part of that district are over-laid by black slates 

 (ai'gillites), under and between these being several layers of chert. 

 All such wei-e deposited in a quiet time upon the Archfean granites ; 

 red Huronians. Their stratification is regular, as even as that of the 

 North Toronto clays, and very like it. But the whole country was 

 afterwards shattered by earthquakes ; great cracks would form, as it 

 was cooling, or being folded by differing distribution of pressure, oi- 

 swelled up by volcanic gases ; and through these cracks — 50 to 200 

 feet in width, and miles in length — up rushed lava streams, over 

 flowing the slates for miles around, to a depth varying with the slope- 

 of the surface and the distance from the fissure. I do not know of 

 over 50 feet in depth of lava, but I have heard of 200 feet. Where this, 

 lava sheet has been glaciated or otherwise worn away, the matter which 

 filled the cracks often shows above the level, like a wall — so mark 

 edly that these features have received the local name of "rampykes." 

 I have found several of them, and hundreds of miles of country, per- 

 haps thousands, have been deluged with lava through their agency,, 

 but I have found no volcanic pipes — round or nearly so — cores of old 

 burning mountains. The Michigan geologists have remai'ked several 

 intercalated lava beds ; also ash beds. The fact that these are vol- 

 canic formations is so well established that there seems no room left 

 for other theories : it does however appear extraordinary that from 

 the Lake of the Woods eastward to North of Lake Huron, you 

 are constantly finding this capping of diorite, evidence of the fieiy 

 time, and that yet you find no round volcanic vents. 



Then follows another period ; the natural forces locally at work 

 become less imposing, and the earthquake fissures no longer emit 

 molten lava. They are, however, still occasionally foi-med, tearing 

 through granite and chert and slate and trap, but they are from 2 to- 

 10 feet only in breadth, and appear to have become mere drains for 

 the surrounding country ; these are now the rich silver bearing veins 

 of the Thunder Bay district —having become filled up with quartz and 

 si)ar, and in many cases with quantities of native silver and sulpliide,^ 

 with zinc blende, a little galena and some iron pyrites. 



In other neighbouring regions, the trap or lava seems to have 

 aided much in the segregation of copper. When it overflowed a later 



