Gibson: Are Affordances Constituted by the Composition and Layout of Surfaces?

I have described the environment as the surfaces that separate substances from the medium in which the animals live. But I have also described what the environment affords animals, mentioning the terrain, shelters, water, fire, objects, tools, other animals, and human displays. How do we go from surfaces to affordances? And if there information in light for the perception of surfaces, is there information for the perception of what they afford?  Perhaps the composition and layout of surfaces constitutes what they afford.  (Gibson, 1979, p. 127).

So, here is a crucial juncture for Gibson.  He's got all this apparatus about surfaces.  (Sentence 1)  He's got all this talk about affordances.  (Sentence 2) How do they fit together?  (Sentence 3)  Maybe information from surfaces could give you information about affordance? (Sentence 4).  But, how could that work?  Possible answer: The composition and layout of surfaces constitutes what they afford.  (Sentence 5.)

But, the problem is that the composition and layout of surfaces does not constitute what they afford.

The pick-up-ability of a box is not constituted by its surface; it's constituted by what's inside, namely, not having a touch-sensitive explosive device inside.

The walk-on-ability of pond ice is not constituted by its surface; it's constituted by its whole thickness.

The sit-on-ability of a chair is not constituted by its surface; it's constituted by the weight bearing properties of the whole of the components.