I was googling some shit about explosives used in mining and found this picture, which is a cross section of a chunk of land to a depth of about a mile. How the fuck do they make these? How can this stuff be deduced, at all? The article it came from said that some of the lower layers extended over a oval shaped region of 20 miles by 60 miles. How the fuck do geologists find that out when they only dig a few feet down at most?