Lakes have been'more numerous, &c. % 
decompofition of fuch leaves as commonly float on 
the furface of every pool, and aré expofed to the 
air. Their remains, being precipitated along with 
other accidental impurities, have fubfided in form. 
of mud, which has afterwards been covered with 
the vegetation of fucceeding years: Such is the 
internal Rructure of marfhes, where the produce 
of the original lake has alone been employed in 
their compofition. 
But fince it is known, that they contain bodies, 
which are not natives of the water, foreign agents 
have certainly contributed to their formation: for, 
in digging for peat, feveral kinds of trees are difco- 
vered, lying horizontally, at different diftances 
below the furface. They are commonly furrounded 
with the natural foil of the bog, and are rarely 
feen in conta& with its bottom. From this circum- 
ftance it is evident, that the inferior part of the 
fibrous matter was formed before they camé into 
the fituation in which they are found. It fre- 
quently happens that they all lie nearly in one 
direction, and are confined to a particular part of 
the marfh. Some are found; others more or lefs 
decayed. Some are mutilated and broken; others, 
nearly entire. In fine, the entraneous matter of 
afwamp perfectly refembles the refufe of a river | 
flowing through a woody country. In the north 
of England, it confifts principally of oak, ath, fir, 
feveral fpecies of willow, birch, and alder. Befides 
thefe, a great variety of leave# are dug tip, with 
B hazel 
