C1636 Embarrassment

"There is a mine?"

Ning Leng couldn't help but exclaim. They were not ordinary people. Everyone knew what a mine meant. Not to mention that the three provinces and nine prefectures near the northern border had discovered the Stone Mine (煤矿), which directly increased the fighting strength of the Great Ning's army.

The Stone Mine (煤矿) was not very sensitive, but the fiery oil was a deadly thing