This is almost certainly not the right answer but might help put your mind to rest on the subject. Since it's bound up with memories of your father, it would be nice to come as close as we can.
Consider the following:
Dante was the first to sing of heaven and of hell, not as the dreams of mythological fiction, but as the objects of a real faith. He was the first who launched from this promontory on which we stand, into the vast immensity of the universe, traversed the abyss amidst demons and infernal tortures, and mounting afterwards through angelic hosts and undiscovered worlds, gazed with stedfast eye upon the glories of the Highest... Dante was the Columbus who discovered this new world of poesy... Dante probably surpassed even Homer himself.
Edmund Dorr Griffin, in Remains of the Rev. Edmund D. Griffin (1831), p. 335.
I got this from the quotes at the bottom of this page. Take a look at some of the others. There are several from the right time period that say almost the right thing.
The basic sense of the lines ("in the constituency...") is that there is a big gap in the land of some traditional, perhaps mythical, enemies that only art (poetry? music?) can bring us close to (approximate). Still more basically, there is some gap or divide that we can only understand through art.
According to this reference, it looks as if Brudder Bones was published about 1868. The American Civil War was fought from 1861 - 1865. Gaps and divides and long-standing disputes would be a fairly hot topic at the time, one would imagine. (Incidentally, the famous Hatfield-McCoy feud was just getting started at that time.) My guess is that
There was some quote that was current at the time referring to a work like Dante's Inferno or Milton's Paradise Lost or Homer's account of the Trojan war that resonated because of the conflict that America had just gone through. I would guess it said something like the quote above in a more concise form.
Here is a quote from that time period: “No tongue can tell, no mind conceive, no pen portray the horrible sights I witnessed.” This was written by a captain in the Union army, John Taggart, after the battle of Antietam in 1861. It's says the opposite of what we want (he says that art can't approximate) but it shows that this sort of vocabulary was current. For that matter, Luke 16:26 in the King James Bible says this: "between us and you there is a great gulf fixed: so that they which would pass from hence to you cannot;" which sounds pretty unfathomable-abyss-like to me.
The sixties were only fifty years ago. How many of the saying on this page do you recognize? (If you were around in the sixties, ask your kids about them.) The 1860s were 150 years ago and it is doubtful that the author of Brudder Bones was writing with an eye to distant posterity. If we were to see the words that the author had in mind, would we even recognize them as a quote? I wouldn't "bet my sweet bippy" on it.