How did the Champlain Sea help create fertile farmland around Montreal?

The Champlain Sea played a crucial role in shaping the landscape around Montreal by depositing sediments that formed the fertile St. Lawrence River valley.1

Following the last ice age, the region was inundated by this arm of the ocean, known as the Champlain Sea, between approximately 13,000 and 9,500 years ago. As the sea eventually drained due to the uplifting of the continent, it left behind a flat, sedimentary plain. This process created the highly productive, fertile soil that characterizes the St. Lawrence lowlands today.231

The resulting topography, which is wider near Montreal than near Quebec City, provided an advantageous environment for agriculture, supporting a higher density of farms and settlement in the Montreal region.1