(86 = Abstraction of Nitrogen from the Atmosphere. 
ed, is liable to lead to great errors.* It is to be lamented, 
as the progress of knowledge is retarded, that the notion of 
a particular period, for particular products and rocks, should 
exist so strongly in the minds of most geologists, when it is 
unsupported, to med extent given to it, by the facts themselves. 
In of this assertion, I refer’ to their wri- 
to eaters? These remarks are made with the 
view of throwing doubt on the notion of a precise period for 
each of the depositions to be spoken of, and substituting a 
_ limited series of periods, during any part of which, aay one, 
or all of them, according to circumstances, might be produ- 
orth for are less dependent upon time, than u 
i them are sriadesnattbbe depositions for the 
— locality, and time, unless under peculiar circumstances. 
A change of. circumstances might reverse the order of the 
depositions, as sees their locality. In other words, two 
or more depositions of limestone, as regards time, may each 
have their sie panaicda of coal, salt, and the mechanical pro- 
ducts ;. the same locality, exhibiting as fran different pre: 
ducts, as there were successive depositio 
OF COAL. 
» All the coal which is used in commerce, is taken from the 
last rocks of the transition, and the first rocks of the second- 
ary class : for few or no masses of coal, either anterior or 
* The production of mechanical rocks requires that a part of the earth’s 
surface should be be exposed to the acticn of abrading powers. This effect 
would rise to currents, charged with the products of these s. 
Frem these currents, gravel, sand, and mud, would be deposited according 
to their known laws, Whilst this ‘action w was going on, the sea would be de- 
oe its productions ; and the land itself might be producing oe ele- 
of coal. Thus, e saine play or a the same time, we ve 
aes shells, salt, gravel, s nd, and mud, or clay, or marl, pci 2 to “4 
composition ;) ali si Products, by most geologists, are considered to 
differing 
? One of the cau hich to have mainly contributed to mis- 
lead eee seebe bie kind, and colour, 0 of the roc rocks, which accompany these 
2 nticnmal try 
uniiorm tor 
to have been deposited under my same circumstances, and 
at the sa moe pone time. In a memoir, which f am pcpariog, « n the co- 
a of rocks, I hope to place this subject in its pr oper point of view 
