354 GEOLOGY. [CHAP. XXXIX. 



the relative age of the tf Cambrian &quot; and &quot; Silurian &quot; 

 groups. As those strata, called Cambrian, which con 

 tained organic remains, were found to be nothing 

 more than highly disturbed and semi-crystalline 

 Silurian rocks, so I believe the formations called 

 Taconic in the United States, to have claim to no 

 higher antiquity, and to be simply Silurian strata 

 much altered, and often quite metamorphic. 



