60 



down the ground should never be left unoccupied. There is no difficulty in establishing 

 a new forest on ground of good quality and welj protected ; but this is hard, if not impos- 

 sible on soil impoverished or exposed to the heat of the sun or violence of wind. Yet it 

 is the plantation of such land as this which is generally undertaken by Governments. 

 The difficulty is three-fold : — 1. Absence of soil. 2. Want of shade in summer. 2. Cold 

 winds in autumn and winter. Against the first of these, our principal resource is to plant 

 in sufficient quantity those plants which, like the sand grass, by the interlacement of 

 their root-fibres, prevent the nutritive elements of the soil from being drained away by 

 the rains. It is probable that the net of mesh-work formed by their roots will at last 

 solidify the soil, which will also profit by the continuous deposit of clay. After these pre- 

 liminary operations, one can begin to plant trees. 



" The pine, birch, aspen, alder, are well able to bear the heat of the sun, and should 

 be planted first, then the oak, witch-elm, etc., in their shade." 



It will be valuable for our purpose to notice Mr. Marsh's statement respecting 

 snow : — 



" Whenever the humidity of the atmosphere in contact with snow is above the point 

 of saturation at the temperature to which the air is cooled by such contact, the superflu- 

 ous moisture is absorbed by the snow or condensed and frozen upon its surface, and of 

 course adds so much to the winter supply of water received from the snow by the ground. 

 This quantity, in all probability, much exceeds the loss by evaporation, for during the 

 period when the ground is covered with snow, the proportion of clear dry weather 

 favourable to evaporation, is less than that of humid days with an atmosphere in a condi- 

 tion to yield up its moisture to any bibulous substance cold enough to condense it. 



" In our Northern States, irregular as is the climate, the first autumnal snows pretty 

 constantly fall before the ground is frozen at all, or when the frosts extends at most to a 

 depth of only a few inches. In the woods, especially those situated upon the elevated 

 ridges which supply the natural irrigation of the soil and feed the perennial fountains 

 and streams, the ground remains covered with snow during the winter ; for the trees pro- 

 tect the snow from blowing from the general surface into the depressions, and new acces- 

 sions are received before the covering deposited by the first fall is melted. Snow is of a 

 colour unfavourable for radiation, but, even when it is of considerable thickness, it is not 

 wholly impervious to the rays of the sun, and for this reason, as well as from the warmth 

 of lower strata, the frozen crust of the soil, if one has been formed, is soon thawed, and 

 does not again fall below the freezing-point during the winter. 



" The snow in contact with the earth now begins to melt, with greater or less rapidity, 

 according to the relative temperature of the earth and the air, while the water resulting 

 from its dissolution is imbibed by the vegetable mould, and carried off by infiltration so 

 fast that both the snow and the layers of leaves in contact with it often seem compara- 

 tively dry, when, in fact, the under surface of the former is in a state of perpetual thaw. 

 No doubt a certain proportion of the snow is given off to the atmosphere by direct evapo- 

 ration, but, in the woods, the protection against the sun by even leafless trees prevents 

 much loss in this way, and besides, the snow receives much moisture from the air by 

 absorption and condensation. Very little water runs off in the winter by superficial 

 water-courses, except in rare cases of sudden thaw, and there can be no question that 

 much the greater part of the snow deposited in the forest is slowly melted and absorbed 

 by the earth. 



" The immense importance of the forest, as a reservoir of this stock of moisture, be- 

 comes apparent, when we consider that a large proportion of the summer rain either flows 

 into the valleys and the rivers, because it falls faster than the ground can imbibe it • or 

 if absorbed by the warm superficial strata, is evaporated from them without sinking deep 

 enough to reach wells and springs, which, of course, depend much on winter rains and 

 snows for their entire supply. This observation, though specially true of cleared and 

 cultivated grounds, is not wholly inapplicable to the forest, especially when, as is too often 

 the case in Europe, the underwood and decaying leaves are removed. 



" The quantity of snow that falls in extensive forests, far from the open countiy, has 



