GEOLOGY OF THE VICINITY OB" LITTLE FALLS 



9 



seems to have been unequal on different sfdes, and also to have 

 varied locally from place to place. Around most of the Adirondack 

 region the first deposit laid down on the subsiding floor was one 

 of coarse sand, often becoming a coarse gravel and with much 

 feldspar sand at the base. * It was deposited in shallow water 

 in which was sufficiently strong current action to remove all fine 

 mud. This formation is thickest on the northeast border of the 



IDEAL SECTIONS ILLUSTRATING OVERLAP ON A SINKING LAND SURFACE, 

 AVITH MUCH EXAGGERATED VERTICAL SCALE 



Fig. 1 Partial submergence ; sand being deposited 



Fig. 2 More complete submergence ; limestone being deposited above the sand and 

 also on the newly sunlien land surface 



Fig. 3 Almost complete submergence ; shale depositing on the limestone and over- 

 lapping on the old land surface ; the material being derived from some adjoining land 

 area and brought in by currents. 



Adirondacks, thinning thence both westward and to the south, 

 and on the present southwest border was not deposited at all, 

 and is not found within the map limits. The formation which 

 succeeds it elsewhere is here found resting on the old land sur- 

 face. A more detailed discussion of the reason for its absence 

 here will appear on a later page. This formation is known as 

 the Potsdam sandstone. 



Subsidence continuing, the character of the deposit changed 

 and the Potsdam is overlain by a variable thickness of dolomite 

 and limestone beds, the former much predominating and nearly 

 always containing some coarse sand which becomes very prom- 

 inent in some layers. These rocks are peculiar, are not like ordi- 

 nary open sea deposits, and the exact conditions under which 



