34 LOWER AND UPPER SILURIAN FORMATIONS. 



remains of corals, crinoids, and trilobites, held together by- 

 shale, and gives us, in England,* a few obscure traces of fish. 

 It is most remarkable how uniform has been the Fauna of 

 the earth in those primitive ages. Silurian rocks have now 

 been examined in England, Russia, Germany, and North 

 America, with great care ; also in South America, the south- 

 ern part of Africa, and even at the Falkland islands, the very 

 antipodes of Britain ; yet in no place has any essential differ- 

 ence of fossils been detected. Brachiopods, orthoceratites, 

 trilobites, are almost everywhere characteristic fossils. In 

 the Alleghany mountains, in the hills of Herefordshire, on 

 the slopes of the Ural chain, which divides Europe from Asia, 

 we have remains of the same animal tribes. ( 18 ) There are 

 differences of species that is to say, the fossils of different 

 regions present certain minor peculiarities but even this is 

 only partial, and does not materially interfere with the general 

 fact that there has been a remarkable uniformity of life in 

 the primeval seas. In the present era, it is hardly necessary 

 to say, the case is very different. Even seas so near as the Red 

 Sea and Mediterranean, present wholly different genera of 

 mollusks. It has been thought that there might be a cause 

 for the greater uniformity of life in those ages, in the greater 

 uniformity of temperature, resulting from the as yet unspent 

 heat of the surface, arising from the internal incandescence ; 

 but perhaps the more probable cause was simply the compa- 

 rative newness of life upon earth, and its little experience of 

 those external agencies by which it is liable to be affected, 

 and which, we shall see reason to believe, have operated in 

 producing the many shades of variation which now mark the 

 organic kingdoms. 



