ADIRONDACK MAGNETIC IRON ORES * 9 



2000 feet, to the St Lawrence. The valley of the St Lawrence in 

 this section has been worn down through the Paleozoic strata 

 exposing the underlying crystallines in belts that extend to the 

 river itself. 



The history of the Adirondack topography is very involved. 

 The mountains were upraised and folded long before Potsdam 

 time, while they have been since subjected to long cycles of erosion 

 and to renewed uplifts. The whole region appears to have been 

 planed nearly level in the early Cambric period. It probably par- 

 ticipated in the general Appalachian upheaval and has subse- 

 quently undergone more or less movement. Local faults have mod- 

 ified the erosional features, giving rise to abrupt rock scarps, serrated 

 ridges which appear to be due to block tilting, and to wild passes 

 and gorgelike valleys. The numerous belts of crystalline limestone 

 that are interf olded with the other crystallines have also influenced 

 the development of relief by their more rapid wear. The valleys 

 floored by the limestone always have a rounded open character, in 

 contrast with the usual narrow steep sided valleys found in the 

 gneiss. 



The Labrador ice sheet invaded the Adirondacks from the north- 

 east and north, scoured the ridges to the summits and removed the 

 products of rock weathering that must have accumulated in great 

 thickness during the long period in which the region had been 

 exposed to subaerial decay. Residual sands and clays from the 

 decomposition of rocks in place are practically absent. In turn 

 the ice spread over the region enormous quantities of transported 

 materials — boulders, gravels, sands and clays. The preglacial val- 

 leys are often buried beneath hundreds of feet of such materials. It 

 is to obstructions of this kind that many of the lakes, which afford 

 one of the most attractive scenic features of the Adirondacks, owe 

 their existence. 



The mineral deposits constitute one of the main industrial 

 resources of the region. They are perhaps second in importance 

 only to the forests, as measured by value of the output. In 

 addition to the iron ores, there are workable deposits of talc, 

 graphite, garnet, feldspar and pyrite in different parts of the region. 

 The quarry materials, of which there are inexhaustible supplies, 

 include granite, syenite, anorthosite, trap, limestone and marble, 

 suitable for building, construction or ornamental purposes. 



