Chalk is a kind of limestone, chalk such as the chalk of the Chalk Group, the stone underlying much of southern England, under the Channel, the Netherlands, parts of the North Sea, and down into Champagne. It's also the name of a town in Kent, Chalk, reading about which, thanks to a prompt from ladybird97, is what reminded me to check on Limehouse's origins today and started this whole chain of connections.
Later, yesterday, after seeing the North-West Passage exhibit at the National Maritime Museum (CanCon dealt with for the week), and coming back home to burn things, we sipped on a sparkling wine which proclaimed itself argillaceous. Today's lime-browsing reassured me that not knowing how to translate it said nothing about my French and everything about my ignorance of stratigraphy. Argillaceous rocks have clay content. Limestone can be argillaceous, as is the argillaceous chalk marl through which the Channel Tunnel was dug.
Marl is lime-rich mud. In French, it is marne, from which the river and the department in France are surely named - for that's where Champagne, of the chalk-rich soil and sparkling wines is.
Speaking of limes - one of the other kinds - we also wondered why yuzu has become such a trendy fruit in chocolate.