What does Ponyboy mean when he says , "I was supposed to be the deep one" (pg 75)?

Ponyboy says this in chapter 5, while he is hiding out at the church with Johnny and reading Gone with the Wind to pass the time. He is referring to Johnny's understanding of the book which surpasses his own:

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.

Ponyboy is surprised at the way Johnny picks up on the story better than he himself does - even although he is the more educated of the two, and in consequence, might be regarded as being more of a thinker, an intellectual. This is what he means by referring to himself as 'the deep one.' This is the image that he has amongst the gang. No-one else appears to be as literate as he is. The others are all older and tougher, but he is more artistic and dreamy, liking his books and sunsets.

Johnny is similarly sensitive, if not artistic, and under Ponyboy's influence, as he says, he enjoys things like sunsets too. The pretty Soc girl, Cherry Valance, is the only other person Ponyboy remarks he can talk about sunsets to, apart from Johnny. In this chapter Johnny is also impressed by Ponyboy's quoting of 'Nothing Gold Can Stay', Robert Frost's wistful poem on the transience of beauty, purity, and joy.