The British Geological Society map of England and Wales (Sheet 256 North London) shows geology containing three distinct clay types. Tile kiln lane (marked with the small black oblong on the image) boarders London Clay and and Silt and Fine Grained Sand layer. The latter is marked in pink on the map and the London Clay not depicted as it surrounds the entire boardered section shown.
The yellow area is delineated as ‘sand’ by BGS.
This shows as a bright red/brown colour. This was supported by observations during my site visit, and is the reason I am going with the terra cotta’s for clay type in my proposals for six gates project.
I still have work to uncover the history of tile kiln lane and the nature of it’s output, but that is under way.