Conversation so far:
What is Harold Innis' dirt research?
Harold Innis traveled the country himself gathering masses of firsthand information and accumulating what he called dirt experience.
What kind of information was Harold Innis gathering on his dirt experience?
During his travels, Harold Innis supplemented his fur research by gathering information on other staple products such as lumber, pulp and paper, minerals, grain and fish.

Question: When did he start?
Self-contained rewrite: When did Harold Innis start his dirt experience travels where Innis supplemented his fur research by gathering information on other staple products such as lumber, pulp and paper, minerals, grain and fish?