118 C. P. Williams and J. F. Blandy, 



In the Ontonagon region but few fissure veins have been 

 opened, and most of these have a course of from 60° to 70° east 

 of north, varying about 80° from the bearing of the formation, 

 with a dip of from 50° to 60° to the north. An exceptional in- 

 stance is found in the one vein opened on the Douglass Hough- 

 ton property, which was transverse to the line of bedding of the 

 trap, and is necessarily of different origin. 



On account of the variation of the meridional course, as well 

 as the direction in comparison with the bearing of the beds of 

 rock, it is difficult properly to classify the fissure veins of the 

 different districts. An examination of them in connection with 

 the topographical features of the country would seem to point to 

 various causes of occurrence, arising from the method of eleva- 

 tion of the trappean range. The curvature of the range on Ke- 

 weenaw Point around the centre of elevation of the South or 

 Bi^hemian Range, would appear to account for the radial frac- 

 tures, embracing nearly all the veins of the first class, the co ir^-e 

 of the veins changing from E. of N. at the east end of the T' 

 to N. 58° W., at the North American Mine, at the we^t c ^^ 

 the curvature. Variations from the general rule of radia t\^ 

 ture occur, but it is a question whether these cannot be atc\ 

 for by local causes, or whether they are not fractures i 

 the main veins. 



From the North American Mine to a few miles souti 

 Portage Lake the Range holds a very direct course, sliu 

 conspicuous elevations, and the topography of the coui. 

 notes no disturbances in the formation with the exceptioi 

 deep gorge of Portage Lake. In this section no fissure \ 

 the first class have yet been found. 



The fissure veins of the first class in the Ontonagon 1 ' 

 seem to be due to the warped position in which the > 

 forces have left the strata. The range is broken by m. 

 gorges, marked by the passage of the rivers. The best > 

 we have of the warped position is in the division of v 

 between the Flint Steel, and the Ontonagon Rivers, the ^"i^r, 

 the rocks at the east end or in the Flint Steel mine being 3o 

 and gradually rising to about 57° at the National mine near the 

 west end. The small number of fissure veins which have beea 

 opened in this district, and the limited extent of the working 

 upon them will hardly justify any positive assumption with 

 regard to their origin ; we would however instance the North 

 vein of the Minnesota mine as being probably an excellent 

 example, and one which may be found repeated in other section? 

 of the same district. The course of this vein is 60° E. of N. 

 cutting the strike of the strata at its intersection with the con- 

 glomerate bed at a small angle, the angle of intersection being 

 open towards the east. Direct experiments with plastic sub- 



