190 NEW YORK STATE MUSEUM 



A unique but important bit of evidence is found in the west wall 

 of the narrow channel separating Spoon island from Valcour island. 

 A rather high rocky promontory runs about east-northeast some 

 450 meters from the inner beach of Spoon bay. A block about 

 50 meters wide, cut off from the end of the promontory by a north 

 and south fault, has been converted intO' an island, namely Spooo 

 island, by erosion along the fault plane. Since the rocks dip south- 

 erly, and as the downthrow was on the east, Spoon island has ap- 

 parently been shifted 100 meters to the north and forms a distinct 

 barrier to currents moving easterly along the south wall of the bay. 

 The imprisoned glacial ice and till of the Spoon bay basin would 

 (thus find their nearest and lowest southerly outlet lying along this 

 fault channel, which is about 30 meters wide with high and nearly 

 vertical walls on either side. The ice and till finding its exit here 

 would be forced through under great pressure. 



The northerly position of Spoon island with reference to the 

 present end of the promontory soon allowed the till stream a ' free 

 passage across the south end of the island to deeper and freer 

 channels, and this eastward deflection was hastened by a well marked 

 buttress on the middle of the east wall of the promontory. 



That this buttress has been subjected to great pressure from the 

 north is clearly shown by nearly horizontal pressure joints which 

 cut diagonally across the beds and curve upwards as one follows 

 them southerly. The caves shown in plate 10 lie just south of this 

 buttress, and tliey must have been protected by it in a very marked 

 degree. The rather small and northernmost member of this series 

 of caves is located in the base of the buttress itself, and the 

 pressure received by its northern wall was great enough to dislodge 

 from it a rectangular block weighing some 300 pounds and thrust 

 it southerly and inward against a filling of till. As the bottom of 

 this cave lies some distance below the surface of low water, while 

 its top is completely covered by high water, the finer material of 

 its glacial contents has been washed away. The thrust-in block, 

 however, still holds a number of imprisoned, glaciated limestone 

 pebbles the size of cobblestones. As the upper and narrower por- 

 tion of this cave is thus shown to have been filled with glacial till, 

 we are again forced to conclude that all of the caves of this series 

 are preglacial and that they have been but slightly modified since 

 glacial times. 



This cave offers very valuable evidence as to the solvent powers of 

 Lake Champlain. Although it occurs in the purer dolomitic lime- 



