The Blue Lias , also referred to as the Lower Lias , dates back to the Late Triassic - Early Jurassic boundary , thus includes the Rhaetian , Hettangian , and lower Sinemurian stages .
Head entity: rhaetian Q530828 26
Tail entity: late triassic Q917293 16 17
Relation (head \u2192 tail): P527
Inverse relation (tail \u2192 head): P361