Origin of the Blue Rocks Block Field and Adjacent Deposits, Berks County, Pennsylvania

Research Article| February 01, 1968 Origin of the Blue Rocks Block Field and Adjacent Deposits, Berks County, Pennsylvania NOEL POTTER, JR.; NOEL POTTER, JR. Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota Search for other works by this author on: GSW Google Scholar JOHN H MOSS JOHN H MOSS Department of Geology, Franklin and Marshall College, Lancaster, Pennsylvania Search for other works by this author on: GSW Google Scholar GSA Bulletin (1968) 79 (2): 255–262. https://doi.org/10.1130/0016-7606(1968)79[255:OOTBRB]2.0.CO;2 Article history received: 20 Feb 1967 rev-recd: 20 Apr 1967 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation NOEL POTTER, JOHN H MOSS; Origin of the Blue Rocks Block Field and Adjacent Deposits, Berks County, Pennsylvania. GSA Bulletin 1968;; 79 (2): 255–262. doi: https://doi.org/10.1130/0016-7606(1968)79[255:OOTBRB]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Blue Rocks (40°36′ N., 75°55′ W.) is a half-mile-long block field on the south slope of Blue Mountain, 3 miles northeast of Hamburg, Pennsylvania. The block field consists of angular blocks of Tuscarora Quartzite 4 inches to 20 feet long. The blocks were derived from strongly jointed quartzite cliffs on Blue Mountain and have moved downslope over the Martinsburg Shale. On two sides of the field of open blocks are forested rubble deposits that contain boulders equivalent in size to those in the block field, but with fine material in the interstices. The rubble adjacent to the block field occurs as gently sloping, step-like terraces with fronts 10 to 30 feet high and slopes of 18° to 22°. The block field is separated from the source cliffs by about a half mile of rubble covered by mature forest.Tabular blocks in the block field have an imbricate structure and describe a series of lobes in which the blocks dip steeply upslope. The blocks are crudely sorted vertically, with coarser material at the surface. Locally, horizontal sorting on a small scale is also apparent.Blue Rocks and the adjacent rubble deposits closely resemble solifluction sheets or terraces on the Seward Peninsula, Alaska. The lack of fine material in the block field probably resulted in part from the flushing of fines after downslope movement ceased.The block field is older than the mature forest on the rubble between the block field and the source cliffs. It was probably formed by solifluction or creep in the periglacial climate of the Wisconsin glaciation, after which removal of fines occurred. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.