Vetch Simpson

Looks like a glaucontitic green sand, some gleying in the clay component, but mostly sandy/silt.

I wouldn't worry about the colour difference - it is the same material, just that the iron oxides as a different colour with relation to the water table.

It might be worth experimenting with various additives and also various other fats with higher melting points. I know that they used to add blood to the earth floors to seal them and i also know that linseed oil can be fairly fickle when it comes to setting/ being absorbed and adsorbed.

Lime might do some weird things with linseed ie mixing an alkali and an oil normally makes soap - not an ideal floor material. It might also depends on the mineralogy of the clay ie a high activity strength clay (ie volcanic) should form a stronger bond than a low activity clay, or a clay from an area high in calcium is going to give a low rate of adsorption.

I suspect that another problem might be getting the sand/clay ratio right to avoid cracking when the clay dries.

If all else fails then a watery mix of pva glue works wonders on dusty things.