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This map dated 1931 shows an area of marsh. Since then its use as a landfill site has turned it into 30 metre high hill. It has now been capped off with soil but such sites continue to generate methane for years afterwards. This manhole is one of the methane vents.
I think these rock filled ditches and embankments are are to catch storm water and prevent big flows which might carry soil away.
Flushing on December 25
Fox Oaks, etc.
Light going. Took busses. Landed up at Woodhaven Boulevard station. Walked west along Jamaica Avenue. Had a drink. Walked further west and caught the or train from 85 Street - Forest Parkway back into Manhattan.
or 
train from 85 Street - Forest Parkway back into Manhattan.
