▁three ▁important ▁boundaries : ▁( 1 ) ▁the ▁south ▁boundary ▁line ▁of ▁Pennsylvania ▁separ ating ▁it ▁from ▁Maryland ▁and ▁Virginia ; ▁( 2 ) ▁the ▁west ▁boundary ▁of ▁the ▁three ▁lower ▁count ies ▁of ▁Pennsylvania ▁( now ▁Del aware ) ▁separ ating ▁it ▁from ▁Maryland ; ▁and ▁( 3 ) ▁the ▁south ▁boundary ▁of ▁the ▁three ▁lower ▁count ies . ▁ ▁The ▁pair ▁also ▁conducted ▁a ▁number ▁of ▁experiments ▁for ▁the ▁Royal ▁Society ▁such ▁as ▁meas uring ▁a ▁degree ▁of ▁longitude . ▁ ▁Mason ' s ▁journal ▁provides ▁the ▁most ▁complete ▁record ▁of ▁the ▁survey ▁and ▁its ▁progress . ▁The ▁journal ▁includes ▁his ▁astronom ical ▁observations ▁and ▁personal ▁notes ▁about ▁the ▁American ▁front ier ▁environment ▁and ▁his ▁experiences ▁in ▁colonial ▁America . ▁ ▁Mason ▁and ▁D ixon ▁failed ▁to ▁measure ▁the ▁entire ▁length ▁of ▁the ▁south ▁boundary ▁of ▁Pennsylvania ▁as ▁determined ▁by ▁its ▁char ter . ▁ ▁In ▁the ▁summer ▁of ▁ 1 7 6 7 , ▁the ▁surve ying ▁party ▁crossed ▁the ▁Mon ong ah ela ▁River ▁and ▁the ▁Great ▁C ata w ba ▁War ▁Path , ▁viol ating ▁a ▁treat y ▁limit ing ▁the ▁west ward ▁expansion ▁of ▁English ▁settlement s . ▁ ▁Not ▁wish ing ▁to ▁risk ▁inc iting ▁native ▁host ilities , ▁Mason ▁and ▁D ixon ▁were ▁forced ▁to ▁return ▁east ▁after ▁making ▁their ▁final ▁observations ▁at ▁the ▁cr est ▁of ▁Brown ' s ▁Hill . ▁ ▁Career ▁after ▁the ▁Mason – D ixon ▁line ▁survey ▁After ▁comple ting ▁the ▁boundary ▁survey ▁in ▁the ▁United ▁States , ▁Mason ▁returned