That trench in the street full of cobblestones reminds me of this other picture... New York circa 1908. Presbyterian Building, Fifth Avenue and West 20th Street.
In which they are digging a trench and filling it with similar cobblestones. I don't believe it was for drainage, as the one above is in the crown or high point of the road. Drainage would occur near the curb. But I can't even speculate on what they might have buried. Apparently they didn't have the ability to put it back the way they found it.
Who said anything about filling a trench with cobbles?
Those stones are shaped not natural.
The two uses for them in those photos are infill around the tram tracks and the road edge gutters to direct surface water to drains.
