File:The Quarterly journal of the Geological Society of London (1898) (14778964095).jpg

Identifier: quarterlyjourna541898geol (find matches)
Title: The Quarterly journal of the Geological Society of London
Year: 1845 (1840s)
Authors: Geological Society of London
Subjects: Geology
Publisher: London (etc.)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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e. Someof the most conspicuous features of these glaciers, such as theirfalse-bedding, their differential flow, their apparently rapid advanceand the readiness with which they expand into radial fans, suggestthat their ice is far more mobile than that of the Swiss glaciers.But further acquaintance with the Spitsbergen glaciers led us tochange this opinion, especially in the case of the debris-laden strata ofice. Closer examination showed that the false-bedding was due toshearing. As the glacier presses against its talus-bar, bands of iceare driven forward and ride across the lower layers along thrust-planes. Thus PI. XYII, fig. 2, shows part of the upper face ofBooming Glacier : the face is broken into two by a narrow platform.This ledge marks a band rich in debris, above which is one ofthe thrust-planes. Smaller shearing-planes occur all through thedebris-laden portion of the glacier. Hence the mechanical move-ment of the lower sections of the glacier appears to be due to a o IS a. ^
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Vol. 54.) THE GLACIAL GEOLOGY OF SPITSBEKGEN. 205 series of shearing-planes, owing to the pressure of the ice behind,rather than to a viscous yielding or to the action of continuousfracture and regelation. The overrolling advance of the glaciers affords a simple explana-tion of the origin of the debris-bands and intraglacial material withwhich the lower part of the glacier is so richly charged. Let usconsider the case of a glacier passing over loose materials, such as araised beach. The ice-blocks which form the talus are generallyirregular in shape, and as they fall with some force their projectingcorners are driven into the ground. The blocks are furtherhammered in by the fall of others upon them. When the glacierflows over the talus, the latter is probably first crushed and thenre-solidified, during which some or the underlying earth must getfrozen in with the ice. When this basal layer of ice works upward,it carries with it the material which it has picked up from thevalley-floor.

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