You will give us your best review, eh Civ???
Sortof of an aside, but could not the area in question(around the great lakes) have been under several hundred/thousand feet of glacier at the time of this event/impact? IOW, if a comet/whatever hit a huge block of ice, what would have been the result? Amongst other things, lots of ice cubes, with some really big ones, thrown around downstream. Just thinking out loud -- so to speak.
I'm not sure, since I've not read much of it. I'll review it on Amazon when I finish -- caution, it could be a year or more. ;')