residual soil vs residual clay

residual soil and residual clay both are nouns.

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

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

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

residual soil (noun)	residual clay (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