By Capt. Paul (Eclogite) on Friday, May 25, 2012 - 04:01 pm:
Hmmm let me see....
No Shirley, they are all sandstone; all one rock type.
Almost rowdy! The Jacobsville was laid down over a long period of time in an oxidising environment which gives the red colour. It is thought that later fluid flow through the sandstones followed fractures and joints in the rock. These fluids were very "reducing" in nature so as they flow through, they bleached out the red colour. In other areas, one might see perfectly round white spots in the sandstone with a tiny black dot in the middle. This is caused by micro-organisms in the sand which were also reducing in nature and bleached out the rock.
And actually, the Jacobsville has nothing to do with the Huron Mountains, but rather their source were the now extinct Penokean Mountains further south in central Wisconsin. It is thought that the Jacobsville was laid down on land in a stream/lake environment, also known as a lacustrine deposit.
By Shirley Waggoner (Shirlohio) on Friday, May 25, 2012 - 04:31 pm:
Interesting, Capt. Paul, thank you.
By Lisa R. (Sisugirl) on Friday, May 25, 2012 - 05:21 pm:
Beautiful pictures today. Fascinating geology lesson -- thank you, Capt. Paul! I've not been to see the Jacobsville sandstone cliffs yet, either. (Was car-less in my college days and at the mercy of other drivers.) Will have to get out there to see them one of these days!