Areas on the Anticosti Island and low-lying regions of Quebec and the Maritimes bordering the Saint Lawrence were below sea level.

He did impressive work for the Geological Survey of Canada in the east of the country, and in Quebec in particular, despite handicaps such as lack of aerial photographs or detailed topographical maps.

[2] Formation of the Goldthwait Sea was part of a broader process in what is now eastern Canada towards the end of the Last Glacial Period.

[7] Large amounts of fresh water, including melted ice and precipitation, flowed into the North Atlantic Ocean during the deglaciation.

The sea was able to cover the coastal areas of the Saint Lawrence because the land had subsided under the burden of the ice sheet.

After this, sea levels gradually rose as water from the ice sheet was returned to the ocean, but at the same time the land rebounded, causing a complex sequence of submersion.

To allow for regional variations in the timing of events, Dionne therefore proposes calling the phases Goldthwaitian I, II and III.

There was much sedimentation along the shoreline, with deltas formed at the mouths of the main rivers on the north shore fed by meltwater from the ice sheet on the Laurentian Shield.

[6] By 9,300 years age the ice front had retreated about 8 kilometres (5.0 mi) from the present shoreline in the north coast region between Rivière-Pentecôte and Sept-Îles, as shown by a belt of end moraines.

[1] The sea covered about 25,000 square kilometres (9,700 sq mi) of what is now Quebec, including Anticosti Island, the south of the Saint Lawrence between Lévis and Baie-Saint-Paul, and the north shore between Les Escoumins and Blanc-Sablon.

The difference can be partly accounted for by the ice cap having retreated earlier in the southern area, which would have rebounded further before the sea levels rose.

[13] The bed of the Upper Saint Lawrence Estuary has glacial tills and bedrock covered by upwards of 200 metres (660 ft) of bluish-gray marine clays dating to the Goldthwait age.