ADIRONDACK MAGNETIC IRON ORES 59 



contain between them reentrant bays or valleys of much gentler 

 upward gradient. At the mouth of one of these valleys, yet at the 

 summit of a somewhat steep terrace, is the village of Port Henry 

 on the 200 foot contour. To the westward beyond the terrace 

 the surface rises again quite steeply to the 500 foot contour and 

 higher. The gentlest gradient is south of the village along the 

 valley of McKenzie brook, a line utilized by the Lake Champlain 

 & Moriah Railroad, which brings the ore to the docks. The general 

 valley is abruptly closed on the south by Bulwagga mountain, a 

 steep fault block which fronts Lake Champlain at an altitude of 

 1 100 feet; while on the north, Bald Peak at 2055 and its southern 

 spurs with declining hights for 3 miles, stand between the hinter- 

 land and the lake. In a general way behind this ridge and forming 

 a broad and upward sloping valley lies the heavily drift-covered 

 district containing Mineville, which with its mines is situated at 

 the foot of the inclosing hills at the north. While a few ledges 

 project above the general mantle of sand and boulders within 

 the broad valley, yet there are 2 or 3 square miles without exposures 

 of any kind, and the largest ore bodies themselves must have been 

 at the outset covered by at least 15 or 20 feet of drift. 



If from the summit of some neighboring mountain the observer 

 endeavors to eliminate in his imagination the cover of drift and 

 restore the old bed-rock topography, the valley becomes one of 

 presumably gentle outlines, broken at the foot of many of the 

 elevations by steep and somewhat precipitous ledges. The latter 

 have been in part, no doubt, freshened up by the erosion of the 

 great ice sheet, but they are believed to have been primarily 

 caused by faulting. The broad and open character of the valley 

 is due to the relatively easy erosion of the rock formations lying 

 beneath, since enough exposures can be identified to lead to the 

 conclusion that they were once and probably still are in large part 

 Precambric or Grenville limestones and their associated sedi- 

 ments, whereas the hills are in most though not all cases the harder 

 gneisses which are believed to belong to intrusive masses of rock. 



These general topographic relations are brought out upon the 

 accompanying map [pi. 2]. From it we see that Mineville is on the 

 1200-1360 contours, while the largest mines open on the 1300. 

 This makes it necessary for the railway to climb 1200 feet in its 

 6 miles of track, and since, in the nature of the case, this rise is not 

 evenly distributed, the engineering problem presented is one of 

 some difficulty. Heavy engines adapted to mountain railways 

 are necessary, but as the heaviest traffic is downward, the grades 



