Recently there was long thread about the BCA. I can now post possible answers to some of the questions, such as "Why is the BCA still raising membership prices when there is a significant amount still left in its coffers?"
I can help with "interburden" which is the material that separates the seams/veins/beds that you are trying to mine, generally vertically. The terminology is similar to the "overburden" which is the material above what you're trying to mine, so the burden of material that needs to be removed if you're working down from the surface.
Could an intentionally shaped hole have been a forerunner of shaped charges?
Not realy, apart from insomuch as you are directing a line of fracture.
The shaped charge (Munroe effect) sort of works by focusing the detonation wave upon a particular point. The charge requires a stand off from the "burden" & in solid rock is pretty ineffective, in rather the same way as an adobe charge is - it needs a free face opposite the charge in order to work. Also you need an explosive with a high VOD and density (ie high brissance)- blasting gelatine having the lowest brissance (that I know of) that reliablely is used in such a way. Black powder certainly would not normaly suit the bill.
Breaking line is the line that the block will split along, whether you're using charges or wedges.
Free face is the direction the rock moves in order to split it from the bed - if you have a series of charges then the free face may be the breaking line of the previous block, rather than an exposed face, but the outer one will be exposed.