That's how far New England was under a sheet of ice, and for over a million years! The four great Ice Ages left their marks on the Boston area, and we not only learned about glaciers, but common rocks and minerals as well.
Mrs. Birtwell first showed us a computerized presentation which explained what glaciers were, how they were created, and what they did to the landscape over which they passed.
Then, she taught us the geologic history of the Blue Hills.
When the South Shore Plaza was built in the 1950's, the contractors found trilobites -- ancient animals that went extinct before the dinosaurs even existed -- in a rock formation called the "Braintree Shale". They sort of looked like those roly-poly bugs you find when you lift up a rock -- except these were a foot long!