Page:The Journal of geology (IA journalofgeology11893univers).pdf/98

This page has been proofread, but needs to be validated.
524
THE JOURNAL OF GEOLOGY.

feet in the ice-sheet.[1] Probably some of the englacial drift there was as high as 1,000 feet or more in the ice, but doubtless a larger part was below than above the altitude of 500 feet; and this was on an area where the ice-sheet had attained probably a thickness of 5,000 or 6,000 feet, its lower fifth or sixth part bearing considerable enclosed drift. In like manner the outer portions of the ice-sheet, where its thickness was less, had probably at its time of culmination no englacial drift above its lower sixth or fourth or third part. Whatever boulders and other drift became incorporated in the higher portion of the zone reached by the currents flowing upward would be thence carried forward in some regions, as from the Huronian and Laurentian areas north of Lake Huron to the boulder belts in Illinois, Indiana and Ohio, described by Chamberlin[2] without intermixture with other englacial drift brought into the ice by less powerful currents on all the intervening extent, which in the case mentioned is about five hundred miles."[3]

T. C. C.

  1. ↑ Geol. and Nat. Hist. Survey of Canada, Annual Report, new series, vol. iv., for 1888-89, pages 36-42E.
  2. ↑ "Boulder Belts distinguished from Boulder Trains—their Origin and Significance," Bulletin, G. S. A., vol. i, pp. 27-31."The Nature of the Englacial Drift of the Mississippi Basin," Journal of Geology, vol. i, pp. 47-60.
  3. ↑ The American Geologist, vol. xii, No. 1, July, 1893, pp. 38-39.
This article is issued from Wikisource. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.