286 THE PENOKEE lEOX-BEARING SERIES. 



llieii- (lipping at a high angle (65^) to the north. The whole Penokee series 

 of which the iron formation is a part is exposed in the same fashion. 

 Therefore thousands of feet of the iron member have certainly been car- 

 ried away by erosion. The figure assumes that about 2,000 feet have 

 lieen eroded from this member since it was upturned. However, it would 

 make no difference with the argument if this erosion occurred during the 

 time of the uplifting. The upper part of the figure represents the surface 

 of the iron formation and a part of the underlyhng and overlying rocks at 

 some past time. Near the bottom of the figure is the presenkland surface, 

 showing the succession of rocks from north to south which are now 

 actually found. A transition from unaltered cherty carbonates to com- 

 pletely decomposed carbonate is noted. This section is not definitely 

 known to occur at every mine, but it well represents the usual occur- 

 rence in that part of the formation Avhich has been productive in iron ore; 

 that is, the presence of more unaltered carbonate at high horizons than 

 elsewhere and in low horizons little or no unaltered carbonate. At the 

 time wheh the upper supposed land surface was an actual one the present 

 surface would be l)ut little exjiosed to the action of percolating Avater. 

 Water could not pass througli the slates which overlie the iron formation, 

 neither could it get in through the underlying feldspathic quartz-slates. 

 Therefore most of the water wliii'h at that time was able to reach the 

 present land surface nuist have done so by passing down along ;vnd through 

 the layers of the iron formation itself The dotted broken line represents a 

 perpendicular course which the water wovild follow were its passage not 

 deflected l)y the lamiiuv of the rocks, but this water would have a 

 tendency to follow the l)edding, so that, entering the ii'on formation 

 at its upi)ermost layer, it would follow the somewhat irregular course 

 marked as the prol)able line of percolation, and would reach the foot- 

 wall quart/ite at the present surface of the country. It is immaterial 

 to the argument whether this line ought to vary farther from a perpen- 

 dicular than marked oi- not, for in any case neai'ly the whole of the 

 present surface of the iron formation would escape the percolating waters, 

 or, if not tliis surface, some other yet lower down. It is, however, 

 2)robable tiiat the lower horizons of the formation would not thus escape 



