° W) 110 THE SCIENTIFIC HISTORY OF A PLANT. \(L}P 
both disintegration and waste may not be simultaneously taking place in the same rock, or in other 
words, both chemical and mechanical causes operating in unison, and by their union producing great 
effects. 
The action of carbonic acid and water is generally to liberate in a soluble form the alkaline bases, 
Action of carbonic producing frequently as an ultimate product hydrate of silica, before which is often 
acid - formed a soluble silicate. I presume that a descriptive detail of the properties of 
silicic acid would be superfluous; but an experiment of that talented chemist, Lavoisier, deserves 
notice here. 
Silicates are more or less decomposed by the action of hot water ; the opacity of the windows in 
Lavoisier's experiment, hotbeds is an example of this. Lavoisier, on distilling some water froni a clean glass 
vessel, found that it left a residue; on weighing- it, he also found that the glass retort had lost in weight 
what the water had gained : from this experiment, it was obvious that a portion of the silica of the 
glass had been dissolved during the distillation. 
It is needless to enumerate all the substances upon which chemists have operated ; suffice it to say 
that their experiments have had a very extended range, and that they confirm all the statements made by 
those who preceded them in this investigation. In this memoir there are two points of especial interest. 
Alkalies not so import- O ne i s > that the alkalies are not quite so essential to the disintegration and decompo- 
ant in disintegration as sitiou of mere rocks as it was at first supposed : for hornblende, epitote, chlorite, 
formerly believed. 11 -i-ipt i -, • i i 
and rocks composed mainly ot these substances, underwent rapid decomposition 
by pure as well as by carbonated water, and this without calling in the agency of an alkali ; this 
experiment accounts for the fact that rocks of this kind are often more readily decomposed by meteoric 
agencies than are felspars : it enables us to trace the simple process by which plants are furnished with 
the lime and the magnesia they require, without our having recourse to any mysterious decomposing 
power of the roots of the growing vegetable. The second and most important result is, that potash, 
potash soda and their S0| la, and their carbonates, but especially carbonate of potash, is volatile at a red 
carbonates -volatile at a heat, — that many plants contain much alkali, whereby a very little is found in the 
ashes after incineration. So, by this incineration of the ashes of a plant, according 
to the ordinary rules for the analysis of vegetables, the Professors Rogers' statements show that a very 
large amount of error must not only have been by such analyses introduced, but by them perpetuated. 
The ashes of anthracite, of bituminous coal, of lignite, contain not a trace of alkali, but digestion with 
water previously to incineration reveals to us their presence — thus adding another proof to the vegetable 
origin of coal. 
I have not gone into the minutiae of any actual decompositions which take place during the disin- 
r/se of facts upon the tegration of certain rocks, because my object is more to point out a train of thought 
present occasion. thaa to ^ e \\ upon the facts by which these reflections may be produced. Our facts 
may be likened to the landmarks of the journey, but their attainment is not its ultimate aim. 
Having mentioned that certain plants require soils containing some particular mineral constituent, 
soils influence distri- and that for the most part soils are formed by the disintegration of the parent-rock 
buuon of plants. Q f fae district, it is obvious that these facts, when applied on a great scale to nature, 
must divide and influence vegetation ; for according to the geological conformations of a country is its 
soil, and so is its flora. 
The subsoil is generally in connection with the original rock, by whose wearing away it was 
subsoil. formed, and the soil is in intermediate relation to it, not always having even the 
same colour; for it may be a transplanted soil, or separated from the parent rock by a larger 
amount of gravel, in which case the white subsoil from the chalk, or the yellow from the clays, would 
colour, depth, and fer- not represent the colour of the land's exterior surface. The depth, texture, and 
fertility of a soil is dependent both upon the mineral constituents and the easily 
disintegrating properties of the rock whence it is formed; and it is the physical and mineral, 
more than the geological age of a soil, that conduces to its fertility : old rocks may be barren in one 
place, but fertile in another. 
Geological systems. I think that a glance at the average soils afforded by the different geological forma- 
tions of this country, would tend to illustrate these remarks. 
Passing over the Silurian Si/stem, upper and lower, including the Ludlow, Wenlock, Caradoc, and 
sou of the saurian Llandilo formations, which have been so admirably classified by Sir Roderick 
Murchison, a system which is largely developed in South Wales, Gloucestershire, 
3 "Worcestershire, Shropshire, and Herefordshire, we arrive at a main deposit, the " old red sandstone," p> 
S a most, popular and beautiful description of the fishes of which has been given to us by Mr. Hugh <* 
"DJj Miller, in his work on this formation. "When argillaceous beds alternate with layers of the sandstone, (A 
