Regarding the influence of soil type, i'll put some info of my own.
Brett is right when he says that soil type has a large influence on foundation type.
Most problems (but not all) come from water.
If there's a sandy soil that drain fast, you don't need to care much about the water problem as there's not a lot of clay and the excess water will just drain away.
Of course you have to care about the sand being structural but that's a different problem.
But if you have clay or heavy clay, things are different.
Even if you go below frost line, clay will swell a lot if water gets to it.
If you have a gravel trench / stone foundation, water will flow thru to the bottom clay and cause problems.
In this scenario you need the ditch or the entire footprint set at an angle to drain any water to a lower spot.
If you're on a hill, it's simple, but if you're on flat land and if maybe water tables are high ... you have problems.
That's why concrete has a lot of appeal for modern homo impatiens.
People don't have to think and leave out the attention to details.
Basically, concrete is a soil replacement that's not sensitive to seasonal change.
Since it replaces the excavated soil, water can't (usually) get easily underneath to cause havoc.
But if you have a rubble trench, that's exactly what's going to happen.
Loved the wood building replica on the shake table.
I wish more people in the "norming" business would care ...
Kris, Jay C does not visit these forums since about 2 years ago.
Neither does Bill Bradbury nor Terry Ruth, both which had some solid building background, natural or conventional.
Needless to say, there are a some of us with many questions unanswered and some even unasked ...
Thanks for the drawing T.S. Moss - I agree I would have loved if there could have been a drawing provided like this to explain how such a foundation could be built up, because I also really like the idea but I am also not sure I feel confident I could build one based on the descriptions here. I have discovered that in central europe, traditional "Fachwerkhäuser" (https://en.wikipedia.org/wiki/Timber_framing#Half-timbering) use slightly raised stone foundations that sound somewhat similar but apart from very, very simple pictures (e.g. http://www.hausbaugrundriss.de/files/images/Pfostenbauweise_Fachwerkhaus.gif) it is difficult to find much details about it, even in some of the historic german books I looked. If there is anyone else here who knows about these types of foundations and could provide a drawing or comment on T.S. Moss drawing that would be great. Or if there are some other reference materials in english that would also be great. Also what I don't quite understand how exactly this differs to the types of stone foundations you read about a lot in natural building books ("Making Better Buildings" or "The Cob Builders Handbook"). Especially in The Cob Builders Handbook the auther talks a lot about the importance of draining water.
Put a gun against his head, pulled my trigger, now he's dead, that tiny ad sure bled