PART IV. Die Errors:

Retained Interior Die Breaks: 

Connected to die crack or split

Definition: A retained interior die break occurs when a flake detaches from the die face but, instead of falling off, it
sinks into the surrounding metal.

Depicted below is a large, retained interior die break straddling a split die in an uncirculated 1973-D nickel. Part of Monticello (the building, not the motto) is raised up on a pedestal, and there is an abrupt step-down to the rest of the design. Essentially, the split diverged around the flake at one end, and reunited at the other end. Of course, deep to the flake, the split would have to have been continuous. The flake would probably have been somewhat wedge-shaped if sectioned vertically from north to south. After breaking free, the flake sank into softer surrounding metal, leaving a corresponding raised area on the coin.