geology vs stratigraphy

geology and stratigraphy both are nouns.

Word	Noun	Adjective	Verb	Adverb
geology	Yes	No	No	No
stratigraphy	Yes	No	No	No

As nouns, stratigraphy is a hyponym of geology; that is, stratigraphy is a word with a more specific, narrower meaning than geology:

geology: a science that deals with the history of the earth as recorded in rocks
stratigraphy: the branch of geology that studies the arrangement and succession of strata

geology (noun)	stratigraphy (noun)
a science that deals with the history of the earth as recorded in rocks	the branch of geology that studies the arrangement and succession of strata