Wikipedia tells me that if one were lucky one might find plesiosaur bones in the mix- and that the proper name for the formation is The Hastings Beds.

I hope you have plesiosaurs under your garden.

We have rocks, rocks, and more rocks, as I learned in high school when my parents built an addition on to their house. The whole of coastal Massachusetts is the terminal moraine of the Laurentide Ice Sheet. If you get out to Cape Cod, it is formally called the Outer Lands, which I envy.