210 
FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
into the peat deposit in the form of dust. Peat containing over 
25% of mineral matter (which is commonly spoken of as ash) 
is not worth much for fuel and certain other purposes. 
In texture, peat is more or less fibrous, being least so in the old¬ 
est and most thoroughly decomposed samples, which are rather 
plastic and look much like mud. The color is always some shade 
of brown, varying from light brown (this usually in fresh or imper¬ 
fectly decomposed peat) to nearly black. 
The principal use of peat, like that of coal, is for fuel. This 
and some of its numerous other uses will be discussed in some de¬ 
tail in a subsequent chapter. 
The term muck is often used more or less interchangeably with 
peat. When a distinction is made between them the former is 
usually applied to peat which is dark colored and throughly de¬ 
composed, especially if it contains a large proportion of ash, or is 
used as a soil to grow crops in. When regarded as synonymous, 
peat is the more classical term, and muck the one more used by the 
masses. 
Humus is another substance, sometimes confused with peat. 
But there is one essential difference between them. Humus is 
formed by the slow decay of vegetable matter in places where it is 
exposed to the air most of the time, which allows a part of the 
carbon to oxidize,* and thus increases the concentration of some of 
the other constituents of the plant, such as lime, potash, nitrogen, 
etc., correspondingly. Typical humus is rarely more than a few 
inches deep, while peat often has a depth of many feet. Another 
difference between peat and humus is that the former always con¬ 
tains certain organic acids which prevent the growth of bacteria and 
fungi.f (These, however, disappear or become considerably 
changed when peat is subjected to extensive aeration, as described 
below). 
It should not be inferred from all this however that a sharp 
line can always be drawn between peat and humus. Although the 
extremes are distinct enough, they often grade imperceptibly into 
each other, either vertically or horizontally. Vertical intergrada¬ 
tion occurs where the upper layers of a peat deposit become exposed 
to the air by being built up above the ground-water level, by the cli ¬ 
mate becoming drier, or by any one of several other causes ; and hor- 
*A certain amount of shade and moisture is necessary for the formation 
of humus, however, for the carbon would be completely oxidized in very dry 
or sunny places, or where fires are frequent. 
fThe reader who is sufficiently interested can find a pretty full discussion of 
humus formation in Chapter 8 of Hilgard’s “Soils,” 1906. 
