*82 the WONDERS OF GEOLOGY. Lect. VIII. 



pseudo-igneous masses and the true ancient primary rocks 

 on which the Silurian strata of Scandinavia rest.* 



In North America a similar succession prevails ; and we 

 have thus proof that the modification, extinction, and 

 renewal of species, are attributable neither to the altera- 

 tion in the course of currents, nor to the elevations or ' 

 depressions of the ocean-bed, nor to other more or less 

 local causes, but depend on some general laws which 

 govern the entire animal kingdom. It is, too, most remark- 

 able, that in Eussia where the deposits have gone on 

 through immense periods without interruption, there are 

 few species which pass from one system into another. 



The Silurian system of North America is divided, as in 

 England, into two groups, which are thus named : — 

 ( Hamilton series. 



Upper Siluman. ) HiUerberg series. 



j Onandaga Salt group 



y Niagara and Clinton group. 



{Hudson river, Utica, &c. 

 Trenton limestone. 

 Potsdam sandstone. 



Silurian strata constitute the grand ranges of the Alle- 

 ghanies ; they appear at the Falls of Niagara, and in the 

 Canadas and Nova Scotia, resting on gneiss and granitic 

 rocks, like the equivalent deposits in Scandinavia. The 

 White Mountains of America are altered Silurian rocks. f 



18. Fossils of the Silurian system. — The remains 

 of upwards of 800 species of animals have been discovered 



* " Whilst Siberia and the Urals were above the waters, Kussia in 

 Europe must have been beneath them ; a conclusion which seems 

 necessary in order to render explicable upon rational grounds the 

 phenomena of the great Scandinavian drift, by which all the low 

 countries of the north have been covered by boulders and far-trans- 

 ported materials." — Geology of Russia. 



f The admirable Geological State Surveys of North America, by 

 Professors Hitchcock, llogcrs, Hall, &c. contain full particulars of the 

 palaeozoic strata and their organic remains. 



