ADIRONDACK MAGNETIC IRON ORES II 



region are now fairly well denned. Professor Kemp has worked in 

 the eastern section including Essex, Warren, and Washington 

 counties and adjacent territory. Professor Cushing has been 

 mainly occupied with the northern region of Clinton, Franklin and 

 Hamilton counties; while Professor Smyth has worked in St Law- 

 rence, Jefferson and Lewis counties on the western side. 



With the publication of topographic sheets for parts of the region 

 by the United States Geological Survey in cooperation with the 

 State Engineer it has been possible recently to undertake the 

 preparation of detailed geologic maps. Thus far Professor Cushing 

 has reported upon the geology of the Little Falls quadrangle in 

 Herkimer county and the Long Lake quadrangle in Hamilton 

 county and Dr I. H. Ogilvie has surveyed and described the Para- 

 dox Lake quadrangle in Essex county. Field work has been 

 completed also upon one or more quadrangles in Essex, Hamilton 

 and St Lawrence counties. 



Outline of geology 



The rocks comprising the Adirondack region are almost^exclu- 

 sively Precambric in age. The bordering Paleozoic strata are 

 sometimes found well within the interior, but they occur in discon- 

 nected exposures which altogether comprise an inconsiderable 

 portion of the total area. Their base, the Potsdam sandstone, 

 rests unconformably upon the Precambric crystalline rocks. The 

 unconformity marks a very long time gap. Before the depo- 

 sition of the Potsdam the Precambric rocks had been modified by 

 repeated dynamic action, had been uplifted, intruded, and finally 

 exposed to erosive influences that removed great thicknesses from 

 their surface. 



The Precambric rocks, with the exception of small dikes that were 

 of late Precambric intrusion, have all been subjected to powerful 

 compression and in many cases have been greatly changed by 

 metamorphism. Among them there are representatives which 

 were undoubtedly original sediments, but these have almost wholly 

 lost the characteristic features of such rocks so that their recognition 

 is at times a matter of extreme difficulty, if indeed they can now 

 be identified at all. The metamorphism took place while they were 

 deeply buried, under conditions of pressure and heat that brought 

 about a recrystallization of the fragmental components; and what 

 were once sandstones, shales and calcareous sediments now have the 

 characters of gneisses, schists and coarsely crystalline limestones. 



