Hachures [noun]

Definition of Hachures:

map line showing height

Engraved lines, especially those used in shading, are called “hatches” or “hachures” (see Hachure).

Between them are incised arks forming hachure parallel to the arks previously mentioned.

These lines seem to indicate the upper edge of an apron which is covered by vertical hachure.

The accompanying hachure maps show them so well that little description is needed.