So when the glaciers arrived the stage had already been set. The graben had produced a valley through which they could flow. Soft sedimentary rocks comprised the bedrock of that valley. Meanwhile, years of rainwater and running water had weakened the bedrock. As the ice sheets oozed through, pushing their layer of rocks beneath them like sandpaper, it was easy enough to deepen the Champlain Valley before filling it with melt water when they finally retreated.
Special thanks to the Lake Champlain Committee for the use of this news article. LCC is a 2,500-member citizens' conservation organization that has been working in New York, Vermont and Quebec for over 40 years to protect the Lake Champlain environment. You can get involved with lake protection by joining LCC. Join online using a web site secure form at: www.lakechamplaincommittee.org) or call (802) 658-1414 for details.