Ok, I looked up marl pit. It is a place where marl is dug. Apparently there is a whole town or industry or something in England. There is a publication named The MarlPit which is:


A village magazine for an area of the Broads, Norfolk
The Marlpit. The community paper for the villages of Coltishall, Horstead and Great Hautbois.

That's what it says right on the front, just like that. I am now intrigued. The Marlpit is very generous in its About Us section and tells us that a marl pit is: "A pit from which marl, a mixture of clay and carbonate of lime, is excavated. Marl is used as a fertilizer, among other things. Marl is a rock containing clay minerals and calcite, commonly mixed with other components such as silt." There is a lot more explanation on the site, including the 1685 mention of its transportation. Marl pits seem to be the sites of runs and hikes. Also  in the Netherlands. 

Now you'd think that would pretty much be it, but there is a thing called The Bone Wars which is about some dinosaur stuff found in marl pits in New Jersey. "Few competitions in the era of modern science have been as lengthy, as dramatic or as pointedly nasty,"says one of the bunch of books on the subject. The dinosaur bones came to the Philadelphia Academy of Natural Sciences. This is the exhibit that's there now. See? All roads lead to Philadelphia.

But when I googled Marl Pit Delaware, I found that it is a road in Middletown. Thus, Marl Pit Closed. If you look at history, marl pits in the USA should all be closed. There is an article in the 1883 New York Times about a drowning of two little ones in a Famingdale marl pit. It was a sad accident, and they were clasped together, their curly locks... It was sad but I do love the writing from 1883.