[TYRRELL] THE GOLD OF THE KLONDIKE 59 
rock to contain an average gold content of at least 1/75 of a cent to the 
ton. What percentage of the gold contained in the original rock was 
saved we do not know; but if nature’s concentration processes were not 
erossly inefficient the average gold contents of the gold-bearing Pre- 
Cambrian rocks of the Klondike must have been very low. 
