I noted this chimney during an inspection while walking the roof. The tar-like substance is creosote and is a product of the incomplete combustion of wood. The presence of creosote may be an indication of improper operating techniques, low appliance efficiency, cold chimney, or a combination of all three. This product can be hazardous creating a chimney fire if ignition occurs.
With the heating season upon us, ensure to check your wood-burning appliance and components for safe operation.