II^ON ORES OF THE CLINTOX FORMATION I5 



the extraction of salt. Their presence, even if not due to included 

 beds of rock salt, which so far have never been discovered, indicates 

 a high degree of salinity for the waters, that is likely to have been 

 brought about by evaporation in basins shut off from free communi- 

 cation with the sea. The deposition of the Clinton hematites required 

 a similar concentration, as will be explained later in the discussion 

 of their origin. 



The existence of shallow waters, sheltered bays and lagoons re- 

 ■quisite to the accumulation of deposits like those characteristic of 

 the Clinton formation may be considered as indicative of an exten- 

 sive coastal plain stretching southward from the ancient land masses 

 — the Laurentian and Adirondack areas. Such a coastal plain had 

 been built up from wash of the lands during the long interval from 

 Potsdam to Medina time. During the jMedina age there must have 

 been a gradual sinking of this platform with the progress of sedi- 

 mentation, and the subsidence continued into Clinton time, though 

 not on the same scale. 



As to the northern limits of the shore line during Clinton time, 

 there is little information to be gained from present conditions. 

 Since the uplifting of the strata, they have been continuously sub- 

 jected to erosion and their outcropping portions worn back until 

 they are now considerably south of the original limits. It seems 

 scarcely probable, however, that the Clinton beds ever extended so 

 far north as to overlap on the crystallines, since this would involve 

 the removal of more than loo miles of rock on the western end of 

 the belt, between the present line of outcrop and the southern edge 

 of the Canadian Precambric area. 



The materials of which the Clinton strata are composed were 

 derived ultimately from the Precambric crystallines. A small por- 

 tion may have been furnished by the Paleozoic sediments fringing 

 the crystalline areas and previously upraised above sea level. But 

 as these sediments are for the most part low in iron, it is to the 

 Precambric gneisses and schists with their relatively high iron con- 

 tent and extensive iron ore deposits that we must look for the source 

 of the Clinton hematites. The only sedimentary strata of the lower 

 Paleozoic that contain appreciable percentages of iron are the Me- 

 dina and Potsdam sandstones. The crystalline rocks, on the other 

 hand, uniformly carry several per cent of iron oxids, b.^th free as 

 ■magnetite and combined in the silicate minerals, and in the Adiron- 

 dack region they inclose important bodies of magnetite, heuuitito and 

 pyrite. 



