Crawling out from under a rock…
Rockees and Rockettes!
Due to Jerseyman’s persistence in prodding, I must leave my studies to visit this vexing issue if only to cure my own scientific curiosity. This entails leaving my comfort zone to lurk in the land of petrology (i.e., rock origin and history). My real interest is cold climate phenomena associated with unconsolidated sediments. Rocks are of value to my work only because of their use as geological time travelers. Rock positions indicate long-term slope changes and rock surfaces bear scars from blowing sand and ice crystals under ice age polar desert-like climate (i.e., ventifacts).
There are several types of rocks native to southern New Jersey, and a number of exotic stones to large boulders that were scattered across the Pine Barrens, ether transported by strong current or river ice of the proto-Hudson during the Miocene. I present my opinion as to the nature of locally produced clasts, with the caveat that I do not have rocks in my head as my dear, dear friend Jerseyman suggests.
1) Ironstone – an iron rich sedimentary rock. In southern New Jersey, ironstone is associated with cementation of sands and gravels at a water table. Iron oxidizing bacteria are responsible for ironstone formation and the production of the tea-stain colored cedar water. We interpret the presence of foundered ironstone boulders as evidence of permafrost thaw in the Pine Barrens (more at my website).
2) Silcrete – a silica-hardened stone derived from sandy soil (i.e., a duricrust). This very hard rock is locally abundant at higher elevations of the Inner Coastal Plain, but I’ve seen fields of highly weathered silcrete scattered across parts of the Pine Barrens. You see it used in the foundations of various early Colonial structures across South Jersey. It is also known as cuesta quartzite, sarsen stone in Europe (e.g., Stonehenge) – pudding stone if pebbly, and billy rock in Australia.
3) Cohansey Quartzite – a less hard variant of the above sandstone containing seashells within its matrix. It is abundant in Cumberland and Salem Counties. Like silcrete, it was put to use for tool making by aboriginals. Dr. Alan Mounier wrote his recent dissertation on the native use of sandstones in southern New Jersey.
4) Ferricrete – an iron oxide hardened sandstone that formed in soil. Like silcrete above, ferricrete is a duricrust. In Africa and Australia, silcrete and ferricrete as found in close association, both believed to have formed under hot semiarid conditions millions of years ago. Ferricrete is scarce, but can be seen at PAWS animal refuge in Mt. Laurel side by side with silcrete and ironstone (see below).
French HM, Demitroff M. 2003. Late-Pleistocene periglacial phenomena in the Pine Barrens of southern New Jersey: GANJ Field Excursion Guide, October 11, 2003. In Hozik MJ, Mihalasky MJ (eds.). Field Guide and Proceedings, 20th Annual Meeting of the Geological Association of New Jersey, October 10-11, 2003. Trenton, NJ: Geological Society of New Jersey. pp. 117-142.
Friedman M. 1954. Miocene orthoquartzite from New Jersey. Journal of Sedimentary Petrology. 24, 4: 235-241.
Means JL, Yuretich RF, Crerar DA, Kinsman DJJ, Borcsik MP. 1981. Hydrogeochemistry of the New Jersey Pine Barrens. Bulletin 76, New Jersey Geological Survey, Trenton, NJ. 107 pp.
Mounier RA. 2008. The Aboriginal Exploitation of Cuesta Quartzite in Southern New Jersey. PhD dissertation, Memorial University, St. John’s, NFL.
Wyckoff JS, Newell WL. 1992. Silcrete near Woodstown, New Jersey. In Gohn GS. (ed.), Proceedings of the 1988 U.S. Geological Survey Workshop on the Geology and Geohydrology of the Atlantic Coastal Plain. United States Geological Survey, Circular 1059, Washington, DC, pp. 39-51.
Figure 1 The icehouse at PAWS Farm Nature Center in Mt. Laurel, NJ showing Professor Hugh French addressing attendees as to the significance of its walls. The largest darkest red blocks are interpreted as ferricrete, the gray stones silcrete, and the orangey-buff stones ironstone. This photograph was taken by Fred Akers 10/11/03 during the field excursion for the 20th Annual Meeting of the Geological Association of New Jersey – Periglacial Features of Southern New Jersey.
