Blood Meridian's chapter 22 is painfully neglected, I believe, especially its latter part, from the kid's wandering around the San Francisco area to his encounter of the eldress at the rocks at the end of the chapter. Neglected probably because it lacks the action commensurate with many earlier and later scenes, as the kid seems to just meander, and even Sepich's Notes On Blood Meridian tends to gloss over the potential symbolisms.
But the ogdoad of I Ching hexagrams in the preceding post was inspired by the single I Ching hexagram found in this part of Blood Meridian: hexagram #49 - Revolution (Molting), composed of the "lake" trigram ☱ over the "fire" trigram ☲. The I Ching explains the hexagram's image using four words: "澤中有火", which literally translates to, word for word, "marsh middle has fire". This is the phrase that Wilhelm/Baynes chooses to render as "fire in the lake".
The hexagram name is one word: "革", which translates to "molting" and "revolution". The two seemingly disparate translated words are analogous: "molting" means an old shell is cast off abruptly and completely to make way for a new shell, just as "revolution" means an old order is cast off abruptly and completely to make way for a new order. The sense of death/rebirth is present in these two words.
McCarthy uses the exact phrase "fire in the lake" on page 313. The latter part of this chapter marks the "death" of the kid and the "birth" of the man: the kid sees the reflection in the water of fires burning down San Francisco, a "fire in the lake" ("49" as I Ching number and as symbol of San Francisco!), and at chapter's end the kid encounters the eldress at the rocks, merely a shell of a body, an image of "molting", and this particular scene marks the last time the protagonist is called "kid".
The "kid" is experiencing his own "molting", to emerge as the "man", a kind of death/rebirth. A further reading could be, just as when a snake, e.g., molts, it does not always recognize its own shedded skin and might regard the old skin as another snake and might even try to communicate or attack it, so too the kid does not recognize his own skin but believes it to be an eldress!
But the expression "fire in the lake" is not limited to the I Ching. The Book of Revelation uses a similar expression, "lake of fire", and Blood Meridian's chapter 22 contains other references to Revelation. By coincidence ... or not ... both I Ching's "fire in the lake" and Revelation's "lake of fire" express parallel, really identical, meanings: apocalypse/death is not the end, but necessarily entails a resurrection/rebirth.
This thought will be continued in later posts.