Joret line

The Joret line extends from the Channel Islands (including Jèrriais, Guernésiais, and Sercquiais) and across the continent from Granville, Manche to the linguistic border with Dutch in the North of France and Belgium.

[a] It runs approximately west to east through Normandy north of Granville and Villedieu-les-Poêles and divides Manche in two linguistically and separates Calvados and Orne along with Eure; then it curves progressively to the north and ends up approximately south to north in Picardy, where the line runs with the Amiénois and Thiérache, up to the west of Rebecq, Beaumont and Chimay in Belgium, where it separates Picard from Walloon.

Another effect of the palatalizations a bit further to the north but quite parallel was this: A third isogloss, marking a consonantal change unrelated to the others, more or less follows the Joret line throughout Normandy and continues through northeastern France.

It includes all of Picardy, Wallonia, Champagne, Lorraine and a part of Burgundy.

The Joret line affects toponyms in Normandy and Picardy: Cambrai (corresponding to Chambray), Camembert, Carentan (corresponding to Charenton), Caen (Wace gallicized as Chaem).