RADICAL spoiler alert!
I'm assuming you're talking about Flynn's route.
It's true that the end of the route is really hazy and confusing, and the change of style is jarring, (as it has been done by another writer) but not nonsensical.
I believe that this portion of the novel is highly symbolic and requires an understanding of the nature of echo and the rest of the routes, i did this route last so i could at least grasp whatever the hell was going on.
It seems to me that as Flynn burns in the mines, he becomes one with the "victims" of Echo, their minds fusing and intermingling into a supernatural being that (i think) already existed. The memories and acts of the being are reenacted as Flynn AND his possessor, Samuel Ayers are assimilated into the being (rumored to be the socket man)
The wiki affirms that the scenes seen are actually being done by Flynn rather than them being memories, proposing that whatever Flynn becomes is beyond linear time, but its up for debate.
The thing is that Echo is notoriously vague and enigmatic and confirms little to nothing about its supernatural nature, so no certainties should be expected, really.