Meaning of "Molecular"/A River Runs Through It

I was perplexed with Norman Maclean's usage of the word "molecular" in the book A River Runs Through It.

It's on page 35 of the copy I'm reading, the narrator says he doesn't want to stick around to see his brother catch a fish, he'd "rather remember the molecules."

I can't see any meaning beyond my little friends that bond and react. Maybe you can help me out with your interpretation? Let me know if a more complete description of the situation would help.

While I have your attention, if you've read it, what do you think of A River Runs Through It? I'm quite enjoying it.


PS Is is a faux pas to create a topic with two separate purposes (one to ask a word meaning and another to discuss a book)?