78 NEW YORK STATE MUSEUM 



Thus it is more than probable that northern New York under- 

 went erosion during all of the late Paleozoic era and certainly 

 during the Mesozoic era, when an immense amount of Paleozoic 

 sediment and some Precambric rock were stripped off by erosion. 

 By the close of the Mesozoic northern New York was reduced 

 to the condition of a fairly good peneplain with some hard rock 

 masses rising to moderate heights above the general level. 



At the close of the Mesozoic, or the beginning of the Cenozoic 

 era, the great peneplain was upraised and a new period of active 

 erosion was inaugurated to continue to the present time. 



Much of the faulting of the area dates from the time of this 

 peneplain uplift or even later, though it is likely that some dates 

 from toward the close of the Paleozoic era at the time of the great 

 Appalachian revolution. 



Immediately preceding and probably during much of the great 

 Ice age this region, like all the northeastern United States, was 

 considerably higher than now as proved by such drowned river 

 channels as those of the lower Hudson and St Lawrence. 



During the Ice age of the Quaternary period, the area of the 

 quadrangle, in common with all New York State, was buried under 

 a great ice sheet which has left many records such as striae, glacial 

 boulders, moraines, and drift deposits in general. The preglacial 

 topography was not profoundly altered by ice erosion and deposi- 

 tion. The many extinct and existing lakes of the quadrangle were 

 formed either by the actual presence of the ice dam itself or, more 

 commonly, by irregular deposits of drift across old stream channels. 



A subsidence of the land several hundred feet below the present 

 level took place toward the closing stages of the Ice age or im- 

 mediately after it for this latitude, when arms of the sea extended 

 through the Champlain and St Lawrence valleys. 



The most recent movement of the land has been a differential 

 uplift with greater elevation toward the north. At the latitude of 

 the North Creek sheet, this postglacial uplift has amounted to a 

 few hundred feet, the differential character of the uplift being 

 shown by the tilting of certain of the extinct glacial lake deposits. 



ECONOMIC GEOLOGY 



GARNET 



At the time of the field work but one garnet mine was in actual 

 operation within the map limits, but in all there are at least five 

 localities where more or less garnet mining has been carried on 

 as follows: (i) near the top of Oven mountain; (2) one-half 



