residual clay vs residual soil

residual clay and residual soil both are nouns.

Word	Noun	Adjective	Verb	Adverb
residual clay	Yes	No	No	No
residual soil	Yes	No	No	No

As nouns, residual clay and residual soil are synonyms defined as:

residual clay and residual soil: the soil that is remaining after the soluble elements have been dissolved

residual clay (noun)	residual soil (noun)
the soil that is remaining after the soluble elements have been dissolved	the soil that is remaining after the soluble elements have been dissolved