314 Siluria—Present State of Geology. 
but along with the alluvia is deposited not only plants and 
animals of the surrounding country, but also plants and ani- 
mals brought down from the snowy heights by the same river. 
Similar strata found in a fossil state would undoubtedly lead 
the paleontologist to draw erroneous conclusions in regard 
to the climate of the period. We might give similar exam- 
ples, produced by the Gulf Stream, and also by glaciers, ice- 
bergs, and great inundations passing from one country to 
another. May not some of our present fossils that are found 
under a totally different climate from that under which they 
lived, be accounted for in this way ? 
Our-earth was formed according to fixed and definite laws. 
Its rocks, minerals, and fossils have a definite structure, and 
a fixed position ; therefore, erroneous theoretical conclusions 
must ultimately be overturned by the true philosopher. 
The importance of a correct classification and a standard 
nomenclature, all must admit of—we mean a classification 
that will bear the surest of all tests—universality—a clas- 
sification that will show us that the work of Nature is one 
great plan. It is only on some of the minor subdivisions 
of the formations that diversity of opinions among geo- 
logists exist ; all agree on the main principles of classifica- 
tion—on the stratified and unstratified rocks, on the fossili- 
ferous and non-fossiliferous, on the great divisions of the 
formations and their relative age, derived from a know- 
ledge of superposition and organic remains. Our geological 
systems of classification have undergone a gradual improve- 
ment for many years, having passed through the hands of 
Werner, Macculloch, Conybeare, Al. Brongniart, Omalius, 
D’Halloy, De la Beche, Buckland, Mantell, Phillips, Sir 
Charles Lyell, the Rev. A. Sedgwick, and Sir Roderick 
Murchison. We still require much accurate knowledge for 
laying down correct boundary lines of our classification. 
The azoic rocks demand much patient investigation in 
regard to the laws of deposition before we can expect to 
arrive at correct information in regard to the age of these 
non-fossiliferous strata. 
But ere long we will arrive at as fixed and definite 
arrangement of these rocks as we now have of the protozoic, 
