1092 



AMERICAN FORESTRY 



drainage was diverted and the home and tomb of Wash- 

 ington saved from slipping from its bUiff into the Po- 

 tomac River. But the lady regents who manage Mount 

 Vernon may well at their annual May meeting appoint 

 each year a committee to examine the small drainage 

 tunnel which was cut to divert the water from the Wash- 

 ington grounds, and observe carefully that it is doing its 

 duty. Were these the days of soothsayers, one of them 

 might safely prophesy : 



greatest of the earlier catastrophes, known as the Silver 

 Mountain slide, has, along with many others, been mapped 

 and described by the Geological Survey. It covers 12 

 square miles and the amount of rock which crashed 

 down the steep mountain sides can be estimated only in 

 hundreds of billions of tons. 



With the true rock avalanches, it is the younger moun- 

 tain systems, geologically speaking, which are most sub- 

 ject to convulsions. Tho.se of the Himalayas which 



ROCK STREAM AT HEAD OF AMERICAN BASIN 



Great as was this rock flow, in comparatively recent times, there were thousands of others incomparably greater in the early history of the 

 San Juan Mountains in Colorado. The surfaces have been converted into soil and overgrown by forests and the evidences of sliding obliterated 

 to the untrained eye. 



"When the stream which drains Mount Vernon runneth 

 dry. 



Then the ancient home of Washington shall die." 



The landslide areas of Colorado show that in long gone 

 prehistoric ages, comparatively recent geologically but 

 many hundreds of centuries before the first man, there 

 must have been terrific disturbances in these mountains. 

 The evidence is plain that there have been thousands of 

 slides, some of them of enormous magnitude. Possibly 

 the great saber-toothed tiger which ranged the valleys 

 below and the prehistoric animals upon which he preyed 

 may have heard the terrifying roar of the descending 

 rock masses, but man was not present. One of the 



though of course millions of years old are compara- 

 tively recent examples of mountain building, have con- 

 stant slides which would constitute great catastrophes 

 were their slopes and valleys populated. Sir William 

 Conway describes an instance of rock tumbling where 

 the spur of a large mountain mass pitched bodily into 

 the valley below. The front of the mountain had been 

 undermined by springs, and in a twinkling of an eye a 

 large part of the mountain slid down and shot across the 

 valley, damming its river with a lofty wall, and forming 

 a large lake. Masses of rock were hurled a mile away, 

 blocks of limestone weighing 50 tons being sent through 

 the air like huge cannon shots. This slide carried with it 

 at least 800,000,000 tons of rock and debris. Many 



