Simplify the following text for a Grade 9 native English-speaking person.
Original: Later he discovered that Marsh had gone -- behind Cope 's back and made a private agreement with Vorhees : any fossils that Vorhees 's men found were sent back to Marsh at New Haven .
Simplified: Marsh went behind Cope 's back and made a private agreement with Vorhees : any fossils that Vorhees 's men found were sent back to Marsh at New Haven .