Geological History In a Nut Shell

Over a period of many millions of years, ancient weather and glaciers have formed the Don Valley is situated.

• 400 million years ago :  A tropical ocean compressed clay and turned into shale
• Thousands of years ago :   An ice age left a glacial river.  This is the reason for a big amount of clay in the Don Valley. 
• 75,000 years ago :  The glacier deposited huge bolder from the Canadian Shield in the Don Valley.
 

 

(taken from http://ebw.evergreen.ca/about/site/history/)