LES T0BBENT8 DBS AlPES, BY MAB8CHAND. 95 



After glancing at the natural history of motmtams; at their primary 

 condition ; and at modifications of this effected hy aqueons influence, including 

 disLategration by frost ; at the arrest of these by v^etation, and the resump- 

 tion of the operation of these, ■which occurred consequently on the clearing 

 away of forests, <fec., he says, — " There is an action but little observed, but 

 one which goes on with very great activity, in the decomposition of rock — 

 it is that effected by roots. This influence has been studied by Julius Sacks. 

 and reported in his 2Ianuel de Phydohgie tngitole. 



" In twelve days the roots of the jjhaseoltis multijlorus [the scarlet fa'dney- 

 bean] has produced, on polished white marble, great markings, a demi- 

 miUimfetre in depth, like the traces of an engraver's tool : experiments made 

 with other plants, and on other kinds of rock, give similar results. Of 

 these twelve days, sis were taken by the root in reaching the marble, and 

 in the remaining six days these markings were made. It may be inferred 

 that the presence of forests, which develope a great many roots, deeply 

 penetrating the ground, wiU have for its effect considerably to increase the 

 riches of the soil, by expediting the decomposition and disintegration of the 

 rock. If we think of the results /obtained in a few days by the experiment 

 in question, we may form some idea of the influence of forests acting 

 throughout hundreds of years ; and we may be prepared to admit that the 

 rocky subsoil of the forests, although protected against extreme atmos- 

 pheric influences, may be disintegrated, at least as rapidly as if it had 

 been exposed to the direct influence of the atmosphere, through the influence 

 of the roots of trees. It is to this operation we may attribute the gently 

 rounded forms of calcareous rocks covered by the soil of forests." 



Citing next experiments by Thurmann, in which cubes of different 

 minerals, thoroughly dried, weighir^ each 100 grammes, were immersed in 

 water for five minutes, he states that these gave the following results : — 

 Liassic triassic, compact Jurassic, liassic triassic and ooUthic limestones, 

 granite, serpentine, basalt, dolerites, trachytes, ifcc, gave a mean absorption 

 of 0"50 gramme of water. Similar minerals, including gneiss and com- 

 pact marl schist, somewhat disintegrated and changed, gave a mean absorp- 

 tion of 1'50 grammes; limestone stUl further decomposed, ferruginous 

 ooUtes of Mt. Jura, Uassic schists and grits from the Vosges, and eruptive 

 rocks perceptibly changed, a mean absorption of 4 grammes ; variegated 

 grits, green coloured grits, calcareous chalks, gi-avelly clay, and sands, 

 7 grammes ; and clays, Oxford marls, kaolin, an absorption of from 10 to 30 

 grammes. 



These observations he considered indicative of the absorption of water 

 being proportional to the state of subdivision of the material composing the 

 rock ; and the effect he resolved into their hydroscopicity and their capil- 

 larity — the former, the power of each molecule of the rock to retain around 

 it a layer of moisture difficult to withdraw — the latter, the property pos- 

 sessed by many molecules of earth, to retain, in interstices by which they 

 are separated, small globules of water. 



Apart from these, he treats of the permeability of soils as something quite 

 distinct, and existing in very different proportions — as, for example, in 

 ooUtic limestones, which absorb and retain very little water, but which are 

 very permeable by water, through abounding cracks and chinks, and vertical 

 fissures, by which they are subdivided, in consequence of which water 

 falling upon the surface of them does not remain there, but disappears in 

 innumerable fissures. To such chinks the name lesineg has been given. 



