Split-wedged and Split-filled rocks from Carlisle, MA

Went out for a walk with my Friend From Carlisle (FFC) in the woods north of South Str. Driving over there from my house I passed a wet rocky area along Lowell Rd on private property, that I glance into on the way by, thinking "if I went to explore that, the first thing I would hope to see is a split-wedged rock". That is because it is such a common feature of the little rocky, wet areas that dot the landscape here in Massachusetts.

Starting the walk with FFC, we stepped into the woods into a rocky, wet area. Seeing a split rock a few feet away, I went to take a look:We walked around in the pine saplings, uphill a bit to the west and saw a boulder with multiple splits. They were all wedged:[Sorry I did not photo the whole boulder]

Later, I forget where exactly, FFC showed me this split-filled rock:
I wonder why this rock is filled rather than simply wedged? Is it a different phenomenon?

During the course of the walk we saw one rock pile. So these split-wedged and -filled rocks are pretty common in this part of Carlisle.