CENOZOIC TIME — QUATERNARY. 957 



•stones from valley rocks — chiefly trap and red sandstone — and made scratches in the 

 direction of the valley, while the upper ice left similar evidence of its direction of flow, 

 S. 30'^-50° E., in the distribution of bowlders from the I'egion west of the valley. These 

 bowlders, in general, were dropped in the valley, they sinking in the ice till within the 

 valley floio ; so that, in such a case, they prove only that the flow characterizing the upper 

 ice continued part of the way across the Connecticut valley. 



Other examples of valley ice-streams are those of the Merrimac, N.H., of the 

 Winooski Valley in Vermont, and that of Lake Champlain, as proved by the glacial 

 scratches observed by C. H. Hitchcock. 



Transportation and Deposition. 



1. Gathering of material, and its condition. — The ice-sheet received little 

 material from avalanches, that is, through falls of ice or stones from pre- 

 cipitous declivities or overhanging cliffs, except toward its front margin; 

 for, in the maximum stage of the ice, it covered all the mountains, except 

 the highest. The moving mass carried debris for the most part, not from 

 the slopes and summits of emerged ridges, but from those underneath it, 

 against or upon which it rested, and chiefly from the slopes and summits of 

 such ridges rather than from level surfaces. It obtained its load by abrad- 

 ing, plowing, crushing, and tearing from these underlying slopes and 

 summits. It took up the loose earth and stones, abraded the hard rocks, 

 plowed into the soft, and broke and tore off small and large bowlders from 

 the fissured or jointed rocks. 



The ice-mass was a coarse tool ; but through the facility with which it 

 broke and adapted itself to uneven surfaces, it was well fitted for all kinds 

 of shoving, tearing, and abrading work. Moreover, it was a tool urged on 

 by enormous pressure. A thickness of 1000 feet corresponds to at least 

 50,000 pounds to the square foot. The ice that was forced into the openings 

 and crevices in the rocks had thereby enormous power in breaking down 

 ledges, prying off bowlders, and in abrading and corrading. In contrast, 

 the ice of an Alpine glacier has a thickness ordinarily of but 300 to 500 

 feet. 



It gathered little from the lowest parts of the narrower valleys, because 

 of the subglacial stream often present there, and the open space in the ice 

 above it — the ice resting itself in such cases mostly against the sides of 

 the valley. 



Where the fissured rocks were hard, large stones were taken up, some 

 of them hundreds, and occasionally thousands, of tons in weight. But in 

 regions of soft rocks, such as shale, slate, and fragile sandstone, and of rocks 

 easily decomposed, the material obtained was merely sand, earth, or small 

 stones that were readily reduced to earth. Over areas of great extent, 

 therefore, the glacier moved on with little besides the finer debris to dis- 

 tribute. Such facts suggest a reason for the frequent absence of stones and 

 large bowlders from large parts of a glaciated region. 



In consequence of this subglacial method of gathering materials, nearly 

 all transported debris of the glacier was confined at first to its lower part, 



