148 DIFFERENCE OF SOILS. 
with a microscope, will be found to consist of the 
same ingredients, containing, perhaps, minute specks 
of the brown oxide of iron, derived from the pyrites 
or protoxide of iron usually contained in that rock. 
Where gneiss is the prevailing rock, the soil will be 
composed of the same materials, only the mica is 
more abundant. In a mica slate region, we have a 
soil consisting chiefly of mica, mixed with grains of 
quartz. Syenite and hornblende rock produce a dark- 
coloured soil, containing much feldspar and decom- 
posed hornblende, with but little quartz. The soil 
in the neighbourhood of greenstone trap rocks has a 
dark brown colour, containing pieces of the unde- 
composed rock, and is of a soft, loamy character, 
and exceedingly fertile. Where slate rocks prevail, 
the soil is of a blue colour, and forms a deposite of 
tough blue clay when transported by water. In 
limestone countries we can easily perceive that the 
soil is made up of the ingredients of this mineral ; 
its colour, of course, depending on the colour of the 
rock, and the quantity of vegetable matter contained 
in it. Some of the magnesian limestones, or dolo-^ 
mite, decompose very rapidly when exposed to the 
atmosphere ; and we have seen such in Litchfield 
county. Conn., forming, from their disintegrationj 
large beds* of a coarse white sand. 
* It is a somewhat remarkable fact, ascertained by Prof Hitch- 
cock, that it is a rare thing to find in the soil of a limestone country 
any calcareous matter. Restates that out of 125 specimens of; 
£oils from all parts of the State of Massachusetts, and several of 
them from limestone tracts, only seven exhibited any efferves- 
cence v^rith acids, and 3 per cent, was the greatest quantity of 
lime contained in any of them. From numerous experiments, 
he concludes that only one in 30 of the soils of Massachusetts 
contains calcareous matter. Quere : What becomes of it ? If 
lime is a simple substance whose base is calcium (a metal), it is 
very difficult to believe that calcareous matter " is consumed or 
changed," as Prof. H. states to be a fact. Does this fact not 
lend great probability to the supposition that calcium is a gaseous 
compound, and may thus be produced by the secretory organs of 
animals? 
