TAG caver wrote: My question is why does one layer form almost exclusively one type of cave and the other layer forms a different type?
I was going to try to answer your question, but I think the diagram on page 2 of this pdf will explain it better than I could:
http://www.ese.edu.gr/media/lipes_dimos ... /o/183.pdfBasically, impermeable layers like the Pennington caprock collect and funnel water to the limestone strata like the Bangor. When this water finds a fracture, it dissolves a vertical pit. When this water hits another impermeable layer like the Hartselle, it must again flow horizontally until it reaches a weakness in the Hartselle or the surface. Wherever the water can get past the Hartselle, it bores another pit into the Monteagle. This can be in cave, or on the surface. This is why you often see a horizontal cave entrance just above a Monteagle Pit. The example that comes to mind is Honeycutt Cave and Pit above Gourdneck Cave. The water then travels vertically until it reaches the chert beds in the St. Louis and Warsaw Formations. The water again has a hard time penetrating deeper, so it then flows horizontally to a spring entrance. This is why the last part of multi-drop caves is often a crawl or borehole with chert nodules and beds like the final crawl in McBrides.
The Hartselle in Northern TAG (Tennessee) is often a very resistant sandstone and you get the pattern shown in Crawford's diagram. However, further south in Alabama and Georgia the Hartselle is a weaker siltstone, that is often penetrated inside the mountain by the vertical water. This is why your big pits like Incredible, Fantastic, and Surprise are in Alabama and Georgia and not in Tennessee.