THE CENTURY'S PROGRESS IN GEOLOGY 



studied by Murchison and Sedgwick (corresponding in 

 location to the " primary " rocks of Werner's concep- 

 tion) are the surface feature of vast areas in Canada, 

 and were first prominently studied there by William I. 



WILLIAM SMITH, LL.D. 



Logan, of the Canadian Government Survey, as early as 

 1846, and later on by Sir William Dawson. These rocks 

 comprising theLaurentian system were formerly sup- 

 posed to represent parts of the original crust of the earth, 



139 



