A compound sentence contains at least two independent clauses (with no dependent ones; if there is a dependent clause included, then it is a compound-complex sentence). There are two independent clauses in the sentence above: <em> Its proprietor, Roderick usher, had been one of my boon companions in boyhood </em>AND <em>but many years had elapsed since our last meeting.</em>
There are no dependent clauses here - both clauses are independent and can exist on their own.
