I'll eventually formulate an expanded version of the hypothesis, trying to take into account what's being discussed. In the meantime, I thought I'd share some of what I've come across as I've been exploring the world of 19th century technologies for breaking rocks. I've been particularly interested in collecting historic information about the use of gunpowder and dynamite for blasting boulders. Rather than wait until some mythological day when I'll be able to synthesize everything, I'm going to employ the "thinking out loud" method and present the stuff as I find it. I hope to eventually create a summary of general changes in behaviors and technologies for breaking rocks that will provide some context for the Minnesota stone holes. But for now here are a few pieces of raw information.
Philosophical Magazine (1808:99-100)
"About ten years ago an experiment was made in Cornwall upon a loose rock on the surface, and sand was blown out without any effect having been produced: an equal quantity of gunpowder, confined by a small quantity of tamping, broke the rock; which proved that the resistance was far inferior to that of the common mode."
. . .
"M. Pietet, it is said in the same article of the Philosophical Journal for July, has conceived that a more effective explosion for the purposes of mining might be obtained by leaving a partial vacuity, or by the chamber not being completely filled by gunpowder."
The Edinburgh Encyclopaedia (1832:553):
"The process of blasting rocks, or stones, consists in boring a cylindrical hole, about 10 or 12 inches deep, in the rock by means of a chisel for that purpose. The lower part of this hole is filled with gunpowder. The upper part of the hole is then filled up with fragments of stone, firmly rammed together; a hole being left through these materials, by the insertion of an iron rod, which is turned round during the operation of ramming. This hole is next filled with powder, and a match is applied to it in such a manner, that the operator has time to run out of the reach of the fragments of the rock."
Farm Echoes (1883:45-46):
""Has any one present had any experience with Dynamite, or Giant Powder, in clearing rocks from land? If so, will he give us the result"
"Mr. Starr, of Litchfield, can give us some information on that point."
Mr. Starr-- "I will say that I know but very little about this matter, except from results as shown on my fields. A Mr. Parmalee, who makes it his business to blow up rocks with dynamite, passed my place, and I asked him to experiment in one of my fields, which I expect to clear next summer. There were a large number of rocks in the field, such as could not very well be blasted with powder, and I asked him what he could do. . . . I pointed out a rock ten and one-half feet long, five and one-half feet wide, and nine or ten inches in depth--such a rock, as any one will see, would be difficult to blast with powder, because there is not depth enough to drill into it. I took out my watch, and in precisely seven and one-half minutes from the time he began to work the rock was in atoms. . . . I have used many kegs of gunpowder, during my six years' experience, in blasting rocks, and am free to say, that the same amount of work could not have been accomplished with ordinary blasting powder, and the same number, in less than a month."