136 GEOGNOSY AND GEOLOGY. 
18. Occurrence of Fossil Remains. 
Strata are far from always presenting organic remains, these being only 
found in such as have been deposited from water. It is sufficiently evident 
that they cannot occur in igneous rocks, any indications of their existence 
in such localities being entirely accidental. This, deed, is sometimes 
exhibited where abnormal masses stand in immediate contact with normal, 
and include them. A feature of this kind is seen in Radauthal in the Hartz, 
where fragments of sandstone, containing impressions of leaves, are inclosed 
by euphotide. 
Organic remains have been found to occupy a definite relation to strata. 
Thus some are entirely characteristic of certain formations, groups, or 
systems, and even of individual strata. Certain species and genera are 
limited to particular localities, while others are of more general occurrence ; 
they are either mixed up or they lie distributed in a regular manner. 
Animals and plants most generally occur in different strata, the former in 
limestone, the latter in clay, although this relation is not exclusively 
maintained. It not seldom occurs that organic remains, as of shells and 
corals, compose the principal material of entire beds. This is abundantly 
illustrated in the Silurian system of North America and Europe. 
While by far the greater number of fossil remains are evidently very 
different from the recent, there sometimes occur instances, especially in the 
newer strata, of extraordinary similarity. They are, however, in most cases 
specifically different, and of considerably larger size. The few species 
which have been found, both fossil and recent, are of very great interest to 
the geologist. While older petrifactions occur quite universally distributed 
over the surface of the earth, these are found only in restricted localities, 
so that from them we are entitled to infer a climatic difference. The same 
general features of climate must have prevailed all over the earth in the 
earliest periods of her history, nearly the same mean temperature existing 
at the poles as at the equator, or else there could not have been this uniform 
distribution of animal and vegetable life. This is, nevertheless, an 
assumption which is not well established, the reasons both for and against 
being numerous. A very cogent reason against it is the occurrence of the 
elephant and rhinoceros frozen up in the ice of Siberia, which were well 
prepared to resist the cold that is so eminent in that country. A specimen 
’ was found in 1799, with the flesh and hair still perfect, and with remains of 
the arctic coniferee in its stomach. 
Fossils often occur in localities far distant from the places where allied 
forms now exist in a living state, as shown in the above-mentioned instance 
of the European elephas, primigenius, or mammoth. Remains of the lion, 
tiger, hyena, crocodile, monkey, &c., are found in England, France, and 
Germany, where even allied families hardly occur. A remarkable (and 
perhaps still problematical) case is furnished by the occurrence of a petrified 
Juglans cinerea in the Wetterau, the tree being a familiar member of the 
present flora of North America. 
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