What does Pony mean when he says, “I was supposed to be the deep one” in The Outsiders?

Pony is impressed to realize that there is more to Johnny than he thought.

When Pony and Johnny are on the run after the death of Bob the Soc, Pony gets to know Johnny better.  It has been clear that Pony is considered the brains of the greaser gang.  He gets good grades, likes to read books, and is generally a deep thinker.

Johnny brings Pony a book, Gone with the Wind, because he...

Pony is impressed to realize that there is more to Johnny than he thought.

When Pony and Johnny are on the run after the death of Bob the Soc, Pony gets to know Johnny better.  It has been clear that Pony is considered the brains of the greaser gang.  He gets good grades, likes to read books, and is generally a deep thinker.

Johnny brings Pony a book, Gone with the Wind, because he remembers that Pony once mentioned being interested in it.  Johnny thinks that he book will pass the time, and he actually is quite taken with it.

It amazed me how Johnny could get more meaning out of some of the stuff in there than I could--- I was supposed to be the deep one. Johnny had failed a year in school and never made good grades--- he couldn't grasp anything that was shoved at him too fast … (Ch. 5)

Johnny does not know much about the Civil War, the time period in which the book takes place, but he is very interested in the plot and finds deeper meaning in it than Pony thought he was capable of.  He realizes that even though Johnny never did well in school and his teachers thought he was dumb, he is actually quite bright.

When they notice a sunrise, Pony recites a Robert Frost poem that it reminds him of called “Nothing Gold Can Stay.”  Johnny likes the poem and comments that Pony seems to be unique in his family and in the gang.

"Well," I said, thinking this over, "you ain't like any of the gang.  I mean, I couldn't tell Two-Bit or Steve or even Darry about the sunrise and clouds and stuff. I couldn't even remember that poem around them. I mean, they just don't dig. Just you and Sodapop. And maybe Cherry Valance." (Ch. 5)

When Johnny is lying in the hospital about to die, he remembers the poem and tells Pony to stay gold.  This is a reference to the poem because he is telling Pony to stay innocent.  He wants him to get out of the gang life and take advantage of his intelligence to get an education.

Johnny is the perfect example of not judging a person based on looks.  He may seem like he is just a dropout gang member, but in fact he is a deep thinker.  Johnny and Ponyboy are both young men with more to them than meets the eye.