The first two guns that Cat has pictured are identified as bronze Spanish cannons that were cast in Seville in 1856. I can believe the provenance that is given, of the two cannons being presented to the state by the Navy Dept. to honor a Georgian military officer who was involved in the Spanish-American War, but I'm a little incredulous about that casting date. It seems to me that the profile of these barrels and the lower placement of the trunnions on the tube would suggest an earlier date of manufacture.
The St. of GA description is of course way way off. First the cannons shown aren't bronze they are iron, then they are 18th C., not 1856. I suspect the two Spanish bronze cannons were there before scrapping then replaced with some iron tubes found somewhere else. Virtually all the Spanish cannons brought back from the Philippines were fine bronze pieces, no one wanted pitted old iron stuff that we already had in abundance in the US ca. 1900. A little research will pull up the lists of the cannons given to GA from the US, that were distributed to the various states etc. ca. 1900. These lists show most of the markings, the length, bore, name of the gun, etc.
For some strange reason, I had a premonition that the first half of my post might end up preoccupying your thoughts. You know, now that I take a second long look at those barrells with the aid of enlargement I'll be darned if I don't now concur with your opinion. Both of those barrels are evidently made of cast iron; that ammount, and type of corrosion just doesn't seem plausible on bronze, even if one had the certain evidence that the guns had spent a considerable ammount of time buried in the ground or immersed in seawater which is the one feasible way that experts in this field of study think that the 'dreaded bronze disease' can have an affect upon this type of copper based metal. It might seem to a reasonable mind, that the slow and much milder corrosion that would be caused by the fall of 'acid rain' could never be held responsible for this much damage in the time span that an educated guess would alot to this exposure. Doesn't polluted rain's history only extend back less than half a century (I think the first writings and news reports of rain ruining the paint on cars, and destroying trees in Germany's Black Forest would be placed at about that time)? In any case, some time ago, when I contacted the head conservator of one of our military museums he made the analogy that in his opinion, tomato paste had about the same corrosive power that acid rain does, this of course doesn't mean that the acid content in tomato paste wouldn't be harmful if placed, and kept on the surface of a bronze object. I apologize for going off on this tangent, I suppose if truth be told I'm only trying to cover up for my lack of concentration when originally making observations on these barrels (I apparently had "bronze disease" on the brain when I was looking at these two guns, how else could I have come to the silly conclusion that they were bronze painted with black paint). I just looked at the barrels again, and now that you've made it clear to me that they are indeed made of cast iron, I can plainly see the rust spots showing through where the black paint has fallen away; it's amazing how figuratively blind a person can be, even when looking directly at an object of great interest to himself. Anyway, thanks for the correction.
I suspect the two Spanish bronze cannons were there before scrapping then replaced with some iron tubes found somewhere else.
Of course it would be foolish to argue about this, having the understanding that it is conjecture, but let's just for a moment try and imagine this wild scenario: Lieutenant T.M. Brumby is gifted with the two original bronze beauties, and then lets the state display them, but as he slowly comes to the conclusion these guns are actually his personal property, feelings of the rights of ownership overcome him, and he demands to have the barrells back. The two cannons are at this very moment resting under an old unused workbench, their dulled bronze hidden by a dust laden tarp, their bores filled with nesting spiders, and the present owners (relatives of Brumby) know absolutely nothing about neither their history nor monetary worth. Holy Moly, just think of the moolah!