HALF A CENTURY AGO AND TO-DAY. 



33 



the experiments, observations and analysis thereof later attributed to 

 Charpentier, Agassiz, Tyndall, etc. 



Fiuje 20. The quick relative or comparative shrinkage of the Mer 

 de Glace and other glaciers is an effect of the comparatively greater 

 mass and volume of the Mont Blanc range. The inner temperature 

 of a mountain or mountain-group grou's in some proportion to its mass 

 and volume. So general causes of shrinkage must tell most upon 

 the Mont Blanc range, the factor of greater internal heat being 

 super-added. The principal cause of shrinkage is the increasing 

 dryness of the atmosphere consequent upon 300 years of general 

 Alpine deforestation. An air loaded with moisture deposits its 

 moisture in the shape of ice crystals and prisms upon any surface 

 the temperature of which is under freezing point, and if those 

 surfaces are conveniently situated to preserve those icicles which are 

 atmosphere-born and grow day by day to be acral reefs, the found- 

 ation is laid for a glacier. 



Page 21. Glaciers move at a quicker rate along their centre-line 

 because the ice along this line is pressed down by lateral pressure, the 

 result of the gravity of side masses, and of the resistance of the 

 rock-bed which these masses cannot press back outwardl}', ice being 

 an elastic body. 



Page 22. I connect with this page, which contains a most 

 instructive sketch of the Mer de Glace, a description of the influence 

 of vegetation and climate upon the growth and the shrinkage of 

 glacier-areas, in the Alps only. 



The species of pine, popularly called the aroUe, has given its name 

 to the famous Alpine resort, Arolla. This tree is now almost 

 extinct and the few remaining forests of arolles are as much as 

 possible protected against destruction. At one time these forests 

 extended over extremely vast mountain areas, and if their remains 

 are now so difficult to preserve, it is simply because they have 

 exhausted the soil of the Alps, so far as nourishment suited for that 

 type of pine is concerned. 



The arolle forest has a luxuriant undergrowth ; thick and tall 

 mosses cover a damp and thick layer of soil. There are many 

 shrubs growing out of that moss in thick tangled masses, and the 

 general moisture is such that peaty and marshy patches are most 

 frequent. In prehistoric times — and these practically reach, for 

 Switzerland, down to the days of Julius Caesar — the Swiss climate 

 was characteristically damp and warm ; if only a fraction of a degree, 

 on an average, damper and Avaimer than nowadays. The forest 

 belt extended from lake and river banks to the height of from six 

 to seven thousand feet upon the Alpine slopes. It constituted, in 

 its protected subsoil, in its mosses, marshes and shrub tangle, in 

 its continuous tree growth, a vast and ever refilled reservoir of rain 

 and snow water. Vapours and fog rose from it in much larger 

 quantities than at present. During the long periods of wind- 



