220 TRANSACTIONS OF THE HORTICULTURAL 



the fusing point is reached, a large quantity of carbonic gas is given 

 off, after which the fusion goes on quietly. The explanation of the 

 reaction is this: 



The silica or silicic acid of which the sand is composed, is able, 

 with the aid of intense heat, to take from the carbonic acid, the soda 

 which it holds in combination, and unite with it, forming a glassy sil- 

 icate of soda, and leaving the carbonic acid free, as a gas. • If, instead 

 of carbonate of soda, we had used the carbonate of any of the alkalis 

 or alkaline earths, the oxides of the metals, or compounds of any of 

 these, with the stronger acids, the result, with proper variations in 

 manipulation, would have been the same, viz : the formation of a 

 glassy silicate, and the liberation of the acid constituent. Experi- 

 ments like these have led to the enunciation of the following law : 

 " At elevatnd temperatures, silicate acid displaces all other acids." 

 Now, the conditions under which our primitive rocks were formed, 

 were certainly such as would bring this law into operation, and all 

 their mineral bases would have been converted into silicate. This 

 rock, then, must have corresponded closely with our basalts, trachytes 

 and obsidians, which need but time, heat and pressure, to convert 

 them into into granites, syenites and greenstones. 



We see, then, that in this primitive, crystalline rock, all those 

 substances which go to make other kinds of rock, and are destined, 

 in time, to become the nutrient, as well as the supporting elements 

 of our soils, are locked up as silicates, and must be loosed from their 

 bonds before they can be utilized. 



While a series of experiments, conducted at elevated tempera- 

 tures, has shown that, under these conditions, silicic acid has power 

 to displace all other acids, a parallel series, conducted at lower tem- 

 peratures, has shown, that " at ordinary temperatures silicic acid is 

 displaced by other acids,'' and notably, by carbonic acid. 



The earth having cooled to a point which would permit the con- 

 densation of moisture in its atmosphere, rain fell in torrents, carrying 

 with it various corrosive gases absorbed in its descent. This water, 

 falling upon and sinking into the rocks, is able, in consonance with 

 the law just stated, to break up the more unstable silicates, carrying 

 a portion away in solution, and leaving the remainder as a loose 

 powder, readily washed of by the water which flows over the surface. 



It has been proven by experience that the carrying power of 

 water varies as the sixth power of its velocity; that is, if the current 

 of a stream be doubled, its carrying power will be increased sixty- 

 four fold. From this it can be seen that, if a current, bearing sedi- 

 ment, meets with opposition, it will quickly deposit the coarsest par- 

 ticles in its load, then those which are finer, carrying its finest 

 portions farthest from the shore. So it is that, when the material 

 picked up from the surface of the rocks, and carried through creeks 

 and rivers, meets the waters of the ocean, it is assorted into coarser 

 and finer gravels, coarser and finer sands, and clays. 



