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Recause most of Cape Cod ard its neighboring areas are made up 
of deposits formed ty giaciers of tre Ice Age and their meltwaters, 
it is appropriate to corsicer briefly the origin and spread of these 
mighty ice sheets. Discussion of the causes of glacial climate is, 
however, beyond the scope of this report. This picture of the growth 
and exparsion of glaciers is tased partly on our knowledge of the 
behavior of glacial ice wherever it exists today, and partly on in- 
ferences drawn from deposits telieved to be of glacial origin now 
found over broad tracts in tre rmorthern hemispheree 
he 
the close of the Tertiary period, 
rm olimatic conditions throughout 
i) 
i 
: pies a 
ter 2 a interval of rather 
ec rat 
at 
th vous the averaze was everywhere lowered a few de- 
EBYeeSe This initiate colder, moister weather which de- 
veloped into an ice Az weich fell during the winters at high 
altitudes and in rors es was not completely removed by 
summer melting. The excess oF nm year accumulated on top of that 
of the preceding year. racked -down by the weight of snow heaped upon 
it, and altered in its structure by partial melting and refreezing, 
this snow turned to ices The ice began to spread outward or move 
sluggishly downhill, under the weight of increasing accumulations of 
snow, just as do modern giaciers in the Alps or in the Rockies today. 
After thousands of years,the ice had piled up to such thickness that 
large areas of land were biar eed by far-flung sheets of ice like 
those which cover Greenlard and Antarctica today. 
These Fleistocere zlaciers, like their modern counterparts, were 
thickest where the ee egos n of snow had been heaviest, and be- 
came thimer progressively outward. Several such masses, shaped 
like inverted saucer 3 3 
Je 
i i7)) 
ard covering a total of many millions of square 
er Q 
miles,formed in northern 4trerica,Zurope, and Asia and reached thick- 
nesses estimated as " erest BS eee feet at their centerss At the 
same time the Greenland and Artarctic ice fields were thicker and 
thousands of square miles broader under the cold Pleistocene climate 
than they are todaye - it sroule be noted that there were several 
separate ice caps, only two of which had their centers in the polar 
recions, Many peopie have = see caken impression that the ice of the 
polar areas simply expazced ard moved into temperate latitudes during 
the Ice Age, and that it has shrunk since then to its present dimen- 
Siors » 
These j outward in all directions in some re- 
spects ured ona table. Their margins moved 
over the irre ee and extended far into warmer lati- 
tudes. + 
oniy so long as the forward movement 
co ee be melted or evaporated away 
i 
oy 
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Ze} 
cr 
each d azes of thick ice behind them, the ad- 
var.cin up over hills and even in some places 
to cov 
N ruge gathering-grounds of Pleistocene 
