Quiet Valley Living Historical Farm (stroudsburg, Pa)

Recently my family visited quiet valley living historical farm in stroudsburg, pa. Although we went there for the "craft festival" it was the oven that really captured my attention. I talked with the ladies running the oven briefly and had a brief conversation about how I'm in the process of building my own oven. Well actually its been a few years in progress now. I was amazed at how well their oven looked and how well maintained it is. It really motivated me to want to finish my own.

So far, We dug a 4x4 foot hole, filled it back up, made the foundation with cinder blocks... filled the center with sand, purchased fire brick and now its still sitting there. I based everything off of what I read in kiko denzers book but something I really had an issue with was all of the rocks and trying to find the perfect soil to build with. While talking to the ladies at the historical farm I almost got the impression that rocks are ok? It was just a brief conversation however now I'm somewhat baffled. Dont rocks explode when they are heated? Living in the pocono mountains finding the perfect clay to use for my oven just seems impossible. Has anyone else done this in a similar environment? I'm really hoping to finish my bread oven soon, hopefully before the snow hits this season. I'm wondering if a masonry oven might be a better way to go however I did have my heart set on a cob style earth oven. Any helpful advice appreciated! For more on the historical farm please see my blog post. 

External Link to post: http://neo-homesteading.blogspot.com/2010/09/quiet-valley-living-historical-farm.html