Great Social Studies / History links

@ShawnMcCusker: Chronology of US Historical Documents w/ active links #sschat http://t.co/7bd0E8eLWg

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@ShawnMcCusker: Growth Rings – Maps Of U.S. Population Change, 2000-2010 #sschat http://t.co/X9zQ7Mi8Ev

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@ShawnMcCusker: 100 Years of Change | Visual.ly one seriously amazing infographic for class #sschat #edchat http://t.co/1dzfVIn70g

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