Sentence:  ... when a man is going to drive cattle out of the county he has to put a road-brand on them ... It is generally made of letters or figures, or something that won't cross lines, because where they cross they are apt to <WSD>blotch</WSD> and then it's hard to tell what the brand is and who the animal belongs to. 
Meaning of the word marked with <WSD> tags:  To develop blotches, to become blotchy.