Instead of a longer article, I went for one article per structure.
Here are the others:

• Hoof Wall
• Frog & Collateral Grooves
• White Line
• Bars
• Heels & Heel Bulbs
• Coronary Band & Periople Skin

SOLE

The sole is a callous material growing from the sole corium (directly attached to the pedal bone, or coffin bone, or P3) and links to the internal wall through the white line. It can be thin and soft, or thick and hard (the latter is healthier, and the harder / thicker, the drier / rockier the terrain the horse lives on). The healthier the foot, the more you should be able to distinguish 2 types of sole.

The one closer to the frog is actually (vertically) directly under the coffin bone. It should look like the bone it’s protecting, so concave (bowl shaped). /!\ This shape should naturally occur and never be carved out from the foot!

The 2nd type is the sole closest to the wall. It is the “projection” of the pedal bone’s outer boarder. It should look harder, thicker and more calloused, slightly convex (forming an inner horse shoe^^).
Their main functions are protection of the internal structures, mainly the coffin bone, energy dissipation. Although the outer sole (convex one) also shares a weight bearing role (with the inner wall).

  • Thick sole
  • Thin sole
Left is a horse with good sole depth. Right, very thin sole. It can be safely assessed with X-rays. Otherwise, the groove around the frog should give you an indication. Notice how deep is the groove around the apex (top) of the frog on the left, compared to the right.
  • Unshoeing day
  • 2 months later
Notice the difference in texture between the day the shoes were taken off and 2 months later. The scabby looking sole has been smoothened out with 24/7 turnout and mild stimulation.
Exfoliated sole at the 2nd trim.