usualy the red clay type

The verb cerner does mean to sift, but it can mean to be fertilized; another option

Horse stables soil can contain earth, manure, sand, wood chips, etc.

http://durasoil.com/?gclid=CIbxkv6vq5ECFQSOFQodz12Cdw

http://www.joe.org/joe/2007december/tt7.shtml
With high horse traffic, the soil quickly becomes compacted and will no longer support healthy pasture growth.
http://www.portugal-info.net/info/horseriding.htm
Around Vale do Lobo and Quinta do Lago area the soft sandy soil through endless pinewoods makes for very comfortable riding.

"Dirt" is a generic term used in horse racing to refer to the footing surface for outside tracks. The main ingredient of an indoor track surface is SAND. At best, it might be a blend that includes silt, topsoil, and/or peat moss - all types of dirt. It doesn't seem reasonable that it would be made entirely of dirt. Below is a list of indoor track surfaces from http://www.equestrianfooting.com/products.htm

Riding Ring I is **a medium-grain sand that has 2 – 3% silt**. The color is tan to buff. This sand is an excellent and inexpensive material to blend with other sands and amendments.

Riding Ring II is a blend of **two sands that have a wide range in particle size**. This helps the material to be supportive but not compact. **It has 1 – 2% silt** and is a good material to blend with. We find that it is appropriate for almost all riding disciplines.

Riding Ring III is also a blend of **two sands but uses the non-respirable Clear Air Sand as the base of the mix which promotes quick drainage and a low dust footing**.

Clear Air Sand is a non-respirable **fine grain sand that has had the respirable particles removed** and is essentially dust free. It is a white to buff color and has no silt. It is ideal for blending and use in indoor arenas where air quality is a concern and in outdoor arenas where drainage is a problem (it drains in excess of 50 inches per hour).

Clear Air II is another sand that we use in an indoor application. We coat this sand with a heated dust inhibitor that lasts for years and guarantees a virtually dust free environment.

HoofCushionTM Active Recovery Footing System is a riding surface that we developed to actively recover from the impact of the horse’s movement. A blend of **fibers, sand and peat moss** are used to eliminate the problem of ruts and instability in the footing. The fibers act as a “root-system”, stabilizing the footing and wicking moisture down from the surface. The peat-sand blend is a springy base material that is natural to the horse and adds cushion but not rebound.

Indoor Track is a blend of **sand and topsoil** that is used in an indoor track where horses are being galloped and also under an Equicizer (circular horse exercising machine). The material has some cohesion to provide stability but is still cushsiony.

Polo Mix TM is made for indoor polo arenas. It is **a mix of sand, topsoil and peat moss** that is soft enough to cushion legs from impact but supportive enough for twisting, sprinting and sudden stopping

Stall Cushion is a stall floor material that is made of a blend of sand, soil and clay. This material has more cushion and is less abrasive than stone dust or asphalt. It packs well but will still drain.

Custom Mixes The standard blending cost for adding additional amendments to create a custom footing is dependent on the cost of the amendment and the complexity of the blend.