That year, he went to work at the retail drug store of Chapin & Thurber in Providence, where he decided to follow that career.

He briefly looked for opportunities further south, in Kenosha and Chicago, but returned to Milwaukee and bought out the drug store of Henry Fess, on East Water Street, where the Pabst Building would later stand.

Over years, he spent his free time gathering specimens and studying paleontology, often in collaboration with fellow amateur geologist Fisk Holbrook Day.

Greene became a trustee of the Milwaukee Public Museum and a member of the American Association for the Advancement of Science.

[1][4] The collection was later removed from the building, and is now maintained at Lapham Hall on the University of Wisconsin-Milwaukee campus in a compactor storage system and on display in a small museum area.