208 EROSIONS. 



Were it not for these subterranean streams of water which impart to the air * in wells a portion of the 

 heat contained in them, as well as to keep the water at a higher temperature, much inconvenience would be 

 experienced by the accumulation of ice in wells that were exposed to the intense cold of our northern 

 winters. 



I will not tire your patience longer, but make a suggestion of a practical nature, and close this epistle, 

 which is already extended too far. If the preceding theory be correct, those who experience difficulty in 

 keeping ice in houses erected upon a gravelly terrace as is often the case would do well to copy from 

 this example in nature, and, before erecting an ice-house, make an excavation in the earth, and place therein 

 in a slanting direction, like an inverted roof, alternate strata of compact clay and some porous material, 

 like pebbles, and have the clay (or sound plank in its stead) extend beyond the walls of the house to con- 

 duct off the heated air that might arise and otherwise pass up through the porous soil into the ice-house. 

 But if this is considered too burdensome and expensive an operation, I would suggest to those who have 

 gardens embracing clay soil and sandy loams, and would build an ice-house therein, that they put it upon 

 the former, and plant their early peas and watermelons in the latter for the warm air that permeates the 

 porous earth will prove injurious in the one case, but be beneficial in the other. 



Kespectfully yours. 



ALBERT D. HAGER. 



Having shown the character and disposition of the various sorts of loose materials that 

 cover the surface, let us see what marks the rocks exhibit of having been worn down and 

 torn away in order to furnish so much detritus. 



EROSIONS OF THE SURFACE. 



Although the evidence of powerful denudation is everywhere most obvious, in all the 

 hilly parts of New England, yet we must not hence infer that all the valleys and other 

 inequalities were thus produced. For where we find the stratified rocks dipping in oppo- 

 site directions, so as to form anticlinal and synclinal axes, we see proof that the com- 

 mencement of these inequalities was the original tilting and folding of the strata. But 

 since these movements, the work of erosion has been enormously great. Of its amount 

 we can judge better after detailing the facts. 



In treating of the loose materials produced by erosion, we have gone no further back 

 than the tertiary, for since that time the materials have almost without exception been 

 brought into their present forms and positions. But erosions had a far earlier commence- 

 ment, dating from the period of the first consolidation of the strata that are worn away; 

 and a part of the materials thus produced have been used, it may be more than once, to 

 form rocks, which in their turn have been reduced to an unconsolidated state. As far 

 back, then, as the time when the oldest hypozoic and metamorphic rocks were first hard- 

 ened and elevated, we must extend our thoughts, if we would learn how great the work 

 of erosion has been in Vermont. This carries us back an immense period into the past, 

 for some of these rocks are among the oldest on the globe. 



The agents of erosion are somewhat numerous, and ceaselessly active in appropriate 

 circumstances. All the ingredients of the atmosphere oxygen, nitrogen and carbonic 

 acid act directly upon the rocks, producing disintegration at the surface. Oxygen is 

 probably the most efficient agent. 



* Air of a low temperature, coming in contact with water of a higher temperature, is rarified by the additional heat imparted to it, and 

 rises at once and communicates to the atmosphere in the well this acquired heat, and thus it is kept above the freezing point. 



