This is looking north east from 100th Street between Amsterdam and Columbus Avenues. The Ninth Avenue elevated looms over what is now called Columbus Avenue and the peaked roof of the 104th street station is clearly visible in upper left hand corner.
The large pile of rocks and stones in the lower right foreground is the remains of the original Croton Aqueduct of 1842. The aqueduct ran above ground and eventually to a receiving reservoir located between 86th and 79th streets and between 6th and 7th Avenue. This area is now within Central Park and is the site of the Great Lawn. From there the water flowed through pipes to the distribution reservoir located between 41rst and 42nd streets, between 5th and 6th Avenues.
The site is now occupied by the main branch of New York Public Library.
Eventually the above ground aqueduct was placed underground and the structure you see in the photo was rendered obsolete. The aqueduct was a problem for traffic flow on too many streets, and as soon as the aqueduct was no longer used, where it blocked a street it was knocked down. In many cases the stones were used in construction of other structures. Saint Paul the Apostle on 60th Street and 9th Avenue used a good deal of aqueduct chunks in it’s construction.