This is one of a trio of quatrains by the young Clark Ashton Smith (CAS). This one was actually left incomplete with a missing final line:
Naught of the Past is left but memories--
A wreath of withered roses on its tomb
That, keeping yet a ghost of their perfume
[no more written]
While it's intriguing to speculate what the final line might have been, those first three lines are quite powerful by themselves. The "withered roses" retaining "a ghost of their perfume" is quite evocative of lingering memories, and the inclusion of a tomb places this short poem squarely in the thematic world of CAS.