THE OLD RED SANDSTONE. 149 
plants, but not identical with the plants of the Coal Measures.* 
In Scotland, the formation is richly fossiliferous, and the re- 
mains belong chiefly to the animal kingdom. It is richly fos- 
siliferous, too, in Russia, where it was discovered by Mr. 
Murchison, during the summer of last year, spread over areas 
many thousand square miles in extent. And there, as in 
Scotland, the Holoptychius seems its most characteristic fossil. 
The fact seems especially worthy of remark. The organ- 
isms of some of the newer formations differ entirely, in 
widely separated localities, from their contemporary organ- 
isms, just as, in the existing state of things, the plants and 
animals of Great Britain differ from the plants and animals 
of Lapland or of Sierra Leone. A geologist who has ac- 
quainted himself with the belemnites, baculites, turrilites, and 
sea-urchins of the Cretaceous group in England and the 
north of France, would discover that he had got into an en- 
tirely new field among the hippurites, spherulites, and num- 
mulites of the same formations, in Greece, Italy, and Spain ; 
nor, in passing the tertiary deposits, would he find less strik- 
ing dissimilarities between the gigantic, mail-clad megatheri- 
um and huge mastodon of the Ohio and the La Plate, and the 
monsters, their contemporaries, the hairy mammoth of Sibe- 
ria, and the hippopotamus and rhinoceros of England and 
the Continent. In the more ancient geological periods, ere 
the seasons began, the case is essentially different; the con- 
temporary formations, when widely separated, are often very 
unlike in mineralogical character, but in their fossil contents 
they are almost always identical. In these earlier ages, the 
atmospheric temperature seems to have depended more on 
the internal heat of the earth, only partially cooled down from 
its original state, than on the earth’s configuration or the in- 
fluence of the sun. Hence a widely spread equality of 
15 * * See Note K. 
