sentences: sedimentary rocks often have different colored layers
docs: sedimentary is rock. shale is clastic_sedimentary_rock. sedimentary_clay is soil. sandstone is clastic_sedimentary_rock. clastic_sedimentary_rock is sedimentary_rock. sedimentary_rock is rock. slate is sedimentary_rock. shale is sedimentary_rock. sedimentary_rock is stone. people has different_skin_colors