( ( After ( ( the ( Altonian glacier ) ) ( completely ( retreated ( from ( the ( Chicago area ) ) ) ) ) ) ) ( , ( ( the ( time period ) ) ( ( is ( called ( the ( Farmdalian interval ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN After) (S (NP (DT the) (NNP Altonian) (NN glacier)) (ADVP (RB completely)) (VP (VBD retreated) (PP (IN from) (NP (DT the) (NNP Chicago) (NN area)))))) (, ,) (NP (DT the) (NN time) (NN period)) (VP (VBZ is) (VP (VBN called) (NP (DT the) (NNP Farmdalian) (NN interval)))) (. .)))
After the Altonian glacier completely retreated from the Chicago area, the time period is called the Farmdalian interval.
(ROOT (S (NP (NN Period)) (VP (VBZ is) (NP (NP (DT the) (NN time) (NN interval)) (VP (VBN required) (PP (IN for) (NP (CD one) (JJ complete) (NN wave) (S (VP (TO to) (VP (VB pass) (NP (NP (DT a) (NN point)) (VP (VBN called))))))))))) (. .)))