EVOLUTION OF TILL-STONE SHAPES, CENTRAL NEW YORK

Abstract

Research Article| November 01, 1960 EVOLUTION OF TILL-STONE SHAPES, CENTRAL NEW YORK CHAUNCEY D HOLMES CHAUNCEY D HOLMES 208 SWALLOW HALL, UNIVERSITY OF MISSOURI, COLUMBIA, MO. Search for other works by this author on: GSW Google Scholar Author and Article Information CHAUNCEY D HOLMES 208 SWALLOW HALL, UNIVERSITY OF MISSOURI, COLUMBIA, MO. Publisher: Geological Society of America Received: 05 Jun 1959 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1960, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1960) 71 (11): 1645–1660. https://doi.org/10.1130/0016-7606(1960)71[1645:EOTSCN]2.0.CO;2 Article history Received: 05 Jun 1959 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 CHAUNCEY D HOLMES; EVOLUTION OF TILL-STONE SHAPES, CENTRAL NEW YORK. GSA Bulletin 1960;; 71 (11): 1645–1660. doi: https://doi.org/10.1130/0016-7606(1960)71[1645:EOTSCN]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 A total of 3234 unselected till pebbles and cobbles from 27 localities in central New York are of three lithologic types: sandstones, limestones, and shale (including siltstones). The most distant localities are about 20 miles south of the chief limestone outcrops at the Allegheny Plateau escarpment. Changes in size, shape, and roundness with increasing distance of glacial transport show a relative decrease of about 25 per cent in wedge-form and in rhombohedroid stones and a relative increase of more than 100 per cent in ovoids. Other forms show little variation. Although wedge forms tend to be more conspicuously striated than others, the inference is that rounding predominated over faceting, and that prolonged transportation by the middle-latitude ice sheets tended to produce stones of ovoid form rather than wedge shapes as has been claimed. All three lithologic types show these tendencies, but in different degrees depending on relative toughness. Reduction of the larger sizes provided a continuing supply of smaller ones, and gradual depletion of the larger sizes is reflected in the changing cobble-pebble ratio downcurrent from the source outcrops. Here also, rates of change are governed largely by relative resistance. However, with increasing distance of transport, cobbles increase in roundness more than pebbles, indicating less susceptibility to crushing and perhaps a faster rate of rounding. Only about 10 per cent of the till stones attained a degree of roundness greater than 0.4 on Krumbein's scale (c on Holmes's scale). 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.