MEXICO AND ITS ANTIQUITIES. 



621 



center of which is a sieve through which the finer pieces are shoveled 

 into a vault below. These pieces are then carried to the arrastras, 

 flat stones of hard rock kept revolving in a large tub half-filled with 

 water, where they are in twenty-four hours ground to a fine powder. 



The pulverized ore, called lama, is next carried to the patio, a court- 

 yard paved with large flat stones, where it is allowed to accumulate to 

 a depth of about two feet. The muddy mass is then mixed with ma- 

 gistral, or blue vitriol, salt, and quicksilver, and the whole, now called 

 torta, is thoroughly stirred together by the trampling of mules. This 

 process is kept up for seven hours daily, for from two to four weeks, 

 according to the quality of the ore. The torta is then carried to the 

 lavaderos, or large cisterns, where it is washed and stirred by means of 



