Hi, I'm no expert but I guess it depends where you live what the local soil is like. In the northeast by the coast there is a lot of clay soil mud which is ideal for making creamy, sloppy mud.
Also I think topsoil, especially that found in the garden flowerbed, may comprise of different types of soils to aid plant growth such as compost soil and peat soil.
My only offered solution would be dig, add water, stir with a spade, and see what happens. My garden soil is pretty useless and very black and gritty, yet if I head off to the east coast, where there's loads of coastal errosion, the clay mud there seams pretty perfect for wamming with.
I hope that is if some use, like I say, I'm no expert!
Good luck