THE SILURIAN PERIOD. 395 



and Maine. 1 In the Fox Islands of Maine, the Niagaran age of some 

 gneous rocks seems to be clearly indicated. 2 



Close of the Silurian. 



The closing stages of the Silurian were marked by the withdrawal 

 of the epicontinental sea from considerable areas of the eastern interior 

 which had been submerged during the Niagaran. The sea appears 

 to have continued to cover the area of the Appalachian trough. Oo- 

 genic disturbances at this time seem to have been essentially wanting 

 in North America. The geographic changes at the close of the Silurian 

 appear to have been greater than those which occurred during the 

 period, dividing it into epochs and stages, but they were notably less 

 than those which closed the Ordovician. It follows that the Silurian 

 system is less distinctly separated from the Devonian above than 

 from the Ordovician beneath. 



Foreign Silurian. 



In Europe the Silurian strata have a distribution similar to that of 

 the Ordovician, though they are wanting in some regions where the 

 latter are present. As in the Cambrian and Ordovician periods, the 

 continent seems to have been divided into two distinct geographic 

 provinces. Within the northern, the Silurian strata are rather less 

 widely distributed than those of the preceding system, especially in 

 eastern and northeastern Russia. The fact that the Silurian strata 

 do not appear at the surface over wide areas does not indicate their 

 general absence so much as their widespread concealment. They are 

 believed to be widely distributed beneath the younger beds between 

 the Baltic and the Urals, as well as farther east. In most of the north- 

 ern province, outside of Britain the system has been little deformed. 



In the southern province, the Silurian formations are not widely 

 exposed, appearing in small areas only amidst formations of lesser age. 

 In contrast with the Silurian rocks of the northern province, those of 

 the southern are much deformed. 



The Silurian (the name comes from the name of an ancient tribe 

 of Britain, the Silures) formations of Europe, especially of the northern 



1 Williams, H. S. Jour, of Geol., Vol. II, pp. 16-18. 



2 Smith, G. 0. Geol. of the Fox Islands, Me., Rev. Am. Geol., Vol. XIX, p. 214 



