“ The depth of the lake considerably exceeded the captain’s anticipations, though the absence of anything like a talus near the water line already indicated deep water around the entire shore. The depths range from eight hundred and fifty-three feet to nineteen hundred and ninety-six feet, so far as the soundings show, and it is quite possible and probable that depths both greater and shallower may be found. The average depth is about nineteen hundred and forty feet. The descent from the water’s edge is precipitous ”