Original: However, Wegener was unable to demonstrate a mechanism for continental drift, which, combined with his mostly circumstantial evidence, meant that his hypothesis was not accepted until the 1950s, when numerous discoveries provided evidence of continental drift.
Simplified: However, at the time he was unable to demonstrate a mechanism for this movement; this combined with not enough solid evidence meant that his hypothesis was not accepted until the 1950s, when numerous discoveries provided evidence of continental drift.