This picture shows fill from various places being dumped in the Reservoir.
At the bottom right (SE) there is diabase bedrock excavated from the Jersey City courthouse site. This fill was ordered removed by NJ DEP and is now piled up on the sides of the break on the south wall. The city removed part of the south wall for access by large trucks.
At the right, fill from the Greenville rail yards (according to former councilman Bill Gauguin) is piled up in an island that still exists. This fill, which has a lot of Manhattan schist, is likely originally from excavations for the NYC subways and used as fill in Greenville. Just above and to the right (NW) of the island, an outcrop of the underlying diabase bedrock is visible.
At the top (N) is construction debris, still there.