shell-ice

Starting in the grey dawn, for mile after mile we had to haul the sled over crumbly shell-ice that broke through to gravel; and when the shell-ice was done we came to a new bend where a rapid current washed a steep mud bank.

Ten Thousand Miles with a Dog Sled A Narrative of Winter Travel in Interior Alaska Hudson Stuck 1891

At times, for a few hundred yards, the sled would glide with little effort over smooth, polished ice; then would come a long sand-bar, the side of which we had to hug close, and the ice upon it was what is called "shell-ice," through several layers of which we broke at every step.

Ten Thousand Miles with a Dog Sled A Narrative of Winter Travel in Interior Alaska Hudson Stuck 1891