Sentence:  At some of the mines on the great Mother Lode, where hundreds of tons are not unfrequently thrown down at a blast, and where a wide, soft "<WSD>gouge</WSD>" along one wall enables the minder to keep two or three sides of the rock free, and give the powder the greatest opportunity to "lift" without waste of power, the cost of drilling and blasting per ton is so low that a reduction of one-third, even if it could be made, would not greatly affect the general count; ... 
Meaning of the word marked with <WSD> tags:  Soft material lying between the wall of a vein and the solid vein of ore.