TIIEIR DISTRIBUTION. »5 
monocotyledonous orders, Alices, lycopodiaceas, equisetaceas, and cyca- 
dese, but fragments of dicotyledonous plants also occur with them. 
The least ancient group of fossil plants, which are enclosed in strata 
above the chalk, are a mingled suite of monocotyledonous and dico- 
tyledonous tribes, both terrestrial and lacustrine, bearing considerable 
analogy to plants now in existence. The greater number of fossil shells 
are certainly marine, but those which lie in layers amidst the monoco- 
tyledonous plants of the carboniferous formation, belong almost wholly 
to fresh-water genera, now in existence. Other local aggregations of 
fresh-water shells occur in the upper part of the oolitic series of rocks ; 
but a general deposit of this kind occurs among the most recent, and 
contains species very similar to those that now exist. 
The greater portion of the most ancient fossil shells, &c. belong to 
genera now extinct, as the productse, spiriferas, pentameri, orthoceratites, 
trilobites, and many genera of crinoidea ; and on the other hand, the 
least ancient of the fossils, though specifically distinct from existing races, 
are mostly included in the same genera. 
But the most important results to geology, arising from the con- 
templation of organic remains, are founded on a minute scrutiny of their 
specific characters, and a careful register of their localities in the strata. 
It is not enough for the rigid accuracy of modern inquiry, to say that 
a given rock contains corals, shells, and bones of fishes ; but we must 
know the particular species, and determine all the circumstances of 
their occurrence. The more exact and extended our researches on this 
subject become, the more clear will be our statements on the succession 
of created beings, the more certain our applications of zoological prin- 
ciples to determine the relative antiquity of rocks, and the more satis- 
factory our views of the formation of the strata. Works which, like 
the present, profess to describe the rocks and fossils of a particular dis- 
trict lose a large portion of their utility if they are composed without 
reference to general principles. It is in such local catalogues that the 
