Sentence:  The ore is first cobbed and classed into (a) prile, (b) best dredge, and (c) crusher dredge; "a" is finished product; "c" is crushed, jigged, and huddled; "b" is <WSD>dousted</WSD>, or, after reducing in rolls to 8-mesh, dry-sifted in fine mesh hand sieves. 
Meaning of the word marked with <WSD> tags:  To separate dust from ore.