GROUND-ICE WEDGES 



64s 



At the sides of the wedge the markings of the ice are inclined 

 from the vertical and approach parallelism with the sides. Since 

 the growth seems to occur near the center of the wedge, the older 

 lines, though originally vertical, are later spread apart at the top. 

 Oblique sections of wedges will give exaggerated angles of inclina- 

 tion or even curves (Figs. 14 and 15). 



Fig. 12. — A complicated exposure: a, disturbed muck and clay; h, clay; c, peat; 

 at (? a frost crack runs through the turf and ice. 



Fig. 13. — A complicated exposure: a, clay; h, sand; c, peaty detritus, no struc- 

 ture visible; d, peaty detritus. 



In several cases open cracks were seen running down for a few 

 feet into the ice, often being a prolongation of an open frost crack 

 in the tundra above. Once or twice open cracks were seen within 

 the body of the ice, so that a thin sheath knife could be shoved in 

 for several inches (Figs. 9 and 10). Near the edge of a bank these 

 open cracks may become drainage lines for surface waters, so that 

 a tunnel is developed within the ice (Fig. 16) . As the tunnel widens 

 the roof caves in and a deep gully is formed in the bank. These 

 gullies work back and around the polygon blocks, making the 

 neighborhood of an old bank rather difficult walking. 



