sentences: shale is a kind of sedimentary rock
docs: sedimentary is rock. rudaceous_rock is sedimentary_rock. arenaceous_rock is sedimentary_rock. shale is clastic_sedimentary_rock. oil_shale is shale. limestone is sedimentary_rock. sedimentary_rock is rock. shale is sedimentary_rock. sedimentary_rock is stone. humic_shale is shale.