File:The geological history of the Connecticut Valley of Massachusetts - a popular account of its rocks and origin (1921) (14764157141).jpg

Identifier: geologicalhistor00mill (find matches)
Title: The geological history of the Connecticut Valley of Massachusetts : a popular account of its rocks and origin
Year: 1921 (1920s)
Authors: Miller, William J. (William John), 1880-1965
Subjects: Geology Geology
Publisher: (Northampton, Mass. : The Hampshire Bookshop)
Contributing Library: Wellesley College Library
Digitizing Sponsor: Boston Library Consortium Member Libraries

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ice was crowded between the MountTom lava range and the hard granite mountains on the west side ofthe valley. Glacial Deposits. The vast amount of debris transported bythe great ice sheet was carried either on its surface, or frozen withinit, or pushed along under it. It was exceedingly heterogeneousmaterial ranging from the finest clay, through sand and gravel, toboulders of many tons weight. The deposition of these materialsas we now see them took place during both the advance and retreatof the ice, but chiefly during its retreat. Most of the deposits madeduring the ice advance were obliterated by ice erosion, but thoseformed during the ice retreat have been left practically intact exceptfor the small amount of Postglacial erosion. A very extensive ice deposit called the ground moraine issimply the heterogeneous, typically unstratified, unconsolidateddebris from the bottom, interior, and top of the ice which was de-posited mostly during the retreat of the glacier. When it is mostly
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FIG. 23. A GREAT PILE OF LOOSE GLACIAL MATERIAL KNOWN AS A DRUMLIN, LEFT BY THE RE-TREATING GLACIER OF THE ICE AGE. THIS HILL IS ABOUT 150 FEET HIGH AND ONE-FOURTH OF A MILELONG. PHOTOGRAPHED BY THE AUTHOR. The Geological History of the Connecticut Valley of Massachusetts 65 very fine material with pebbles or boulders scattered through itsmass, it is known as ** boulder clay or till. The pebbles or bouldersof the till are usually rounded or facetted and striated as a result ofhaving been rubbed against the bed rock. Such ground morainedeposits are exceedingly widespread at the surface throughout centralwestern Massachusetts except where they have been covered byPostglacial deposits or removed by Postglacial erosion. In factsuch morainic materials constitute most of the soils of the regionaway from the valley floors. An interesting type of glacial deposit is the *drumlin whichis, in reality, only a low, rounded hill of ground morainic materialor till ranging in height up to 150 feet or

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