Barren Island is off the Rockaways and was populated by Irish, Italian and Polish immigrants who took the dead horses from the five boroughs and processed them to make glue, etc. The glass is from a landfill nearby that bled out its garbage in the 40's. All the pieces of glass and garbage on the island are from between the 1880's and the 1950's. The island was shut down in the 1940's.
Kelly Bewn writes much of the same, but I'll give her a shot, too:
Off Floyd Bennett Field near Rockaway, the beach is perpetually awash in the horse bones from the historic glue and fertilized rendering plants that existing at this site from 1850s through the 1920. In the 1950 the adjacent dumb blew it's cap and old bottle, toys, nylons, and various relics from the 30's and 40's landed in the sands of Dead Horse Bay.
Wowzers. Looks like I missed out. If I had gone to this Beach O' Garbage I would have been hoping to find old jars, apothecary looking ones, and other antiquated glass goods. And maybe some remaining Clorox in those bottles to disinfect everything afterward. Real talk though, the beach does yield fabulous materials.