GEOLOGY OF THE LAKE PLACID REGION 63 



map, opposite p. 62, the eastern front of Whiteface for example, 

 tie will be impressed with the amphitheaters, setting back 

 against precipitous walls, that are everywhere present. The 

 same is true of Sentinel mountain about the headwaters of Clif- 

 ford brook. Ice appears to have stood in these recesses and to 

 have worked the sides back to the coimparatively steep walls 

 which confront us to-day. The open space or ' bergschrund \ that 

 usually intervenes as a huge crack between the ice of a glacier 

 and its inclosing w^all, is a place of specially active disintegration 

 of rock. The thaw by day is succeeded by freezing during the 

 night and the walls scale off to a fairly vertical condition with ex- 

 ceptional rapidity. [An amphitheater with steep walls results, 

 which is a favorite form for the Adirondacks, being well shown on 

 Giant, on the Gothics and not a few other peaks. 



The melting of the ice sheet and its retreat, the temporary 

 blocking of lines of drainage and perhaps general submergence of 

 the region led to the production of lake basins, with their attend- 

 ant deltas and sand plains, now a most suggestive feature of the 

 landscape, but observations, as already stated, have not yet been 

 made in sufficient detail to work out their number, succession 

 and relative altitudes. 



MINERAL.© GY 



The larger formations present little that is attractive to the 

 collector of minerals. The labradorite crystals of the anortho- 

 sites occasionally reach such dimensions and perfection of de- 

 velopment as to exhibit the characteristic twinning striations 

 on cleavage faces. Rarely they show^ the characteristic play of 

 colors of the labradorite from eastern Canada. 



The included masses of limestone are much more prolific. At 

 Cascadeville beautiful light green coccolite is distributed 

 through white calcite. Small dark brown or black garnets are 

 associated, but neither the garnet nor the pyroxene possesses 

 good crystal boundaries, as the individuals have the rounded or 

 corroded aspect, so often seen on minerals contained in lime- 

 stone, 



