242 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
The strata which have been thus replaced may have been thin beds 
of impure limestone, or other relatively soluble materials. The con- 
centration of the iron-bearing waters at this horizon, and the conse- 
quent deposition of their iron, was favored by the solubility of this 
replaced bed, and the relative imperviousness of both the underlying 
quartzite and the overlying talcose slates. The iron-bearing waters 
were probably, in part, merely surface waters, coining to rest in drain- 
age basins and there depositing their iron, under favorable conditions 
at points where the decay or complete removal of the talcose schists 
gave easy access to the soluble bed. Part of the ore deposition, how- 
ever, may have taken place through the action of iron-bearing waters 
gaining access to the soluble and pervious replaced beds at some 
point where these were exposed, and following down these particular 
beds, which formed good channels of communication, even under the 
areas where the}' were covered by the impervious talcose slates. It 
will be evident that the resulting ore deposits, in the two cases, will 
differ somewhat in extent. If deposited entirely from surface waters, 
the ore deposits could not extend beyond the limits of the drainage 
basin in which they were laid down. If deposited from waters flowing 
underground, acting under the principles of artesian flow, the deposits 
might have a greater extent, reaching under oilier beds, and it the 
underground structure was favorable, extending beyond the surface 
limits of the minor drainage basin. 
The ore deposits in the Sugar Hill group of mines usually vary 
between 5 and 10 feet in thickness, occasionally passing these limits. 
The ore commonly carries 50 to 55 per cent metallic iron, and about 1 
per cent of phosphorus. 
