The Century slides are the damaging ones. These occur not only at unexpected times but in unexpected places. The Century slide is the deadly one. It usually comes down a course not before traversed by a slide, and sometimes crashes through a forest or a village. It may be produced by a record-breaking snow or by snow-drifts formed in new places by winds from an unusual quarter; but commonly the mass is of material slowly accumulated. This may contain the remnant snows and the wreckage spoils of a hundred years or more. Ten thousand snows have added to its slowly growing pile; tons of rock-dust have been swept into it by the winds; gravel has been deposited in it by water; and gravity has conducted to it the crumbling rocks from above. At last--largely ice--it breaks away. In rushing down, it gathers material from its predestined way. In the spring of 1901, one of these slides broke loose and came down the slope of Gray's Peak. For years the snow had accumulated on a ridge above timber-line. The mass shot down a steep slope, struck the woods, and swept to the bottom about four thousand feet below, mowing down every tree in a pathway about three hundred feet wide. About one hundred thousand trees were piled in wild, broken wreckage in the gorge below. Although a snow-slide is almost irresistible, it is not difficult, in many localities, to prevent slides by anchoring the small snow-drift which would slip and start the slide. In the West, a number of slides have been suppressed by setting a few posts in the upper reaches of slopes and gulches. These posts pinned fast the snow that would slip. The remainder held its own. The Swiss, too, have eliminated many Alpine slides by planting hardy shrubbery in the slippery snowy areas. This anchorage gives the snow a hold until it can compact and freeze fast. Shrubbery thus is preventing the white avalanche! A slide once took me with it. I was near the bottom of one snowy arm of a V gulch, waiting to watch Gravity, the world-leveler, take his next fragment of filling to the lowlands. Separating these arms was a low, tongue-like rock-ledge. A gigantic snow-cornice and a great snow-field filled, with full-heaped and rounded measure, the uppermost parts of the other arm.