There is nothing that comes to mind with those exacting dimensions.

Starker:”Friends and colleagues, I am willing to put my non-dominant hand into the slot I associate with Memory.  Please be prepared to pull me away if it appears I am in distress.”

<rolls up his sleeve and places his left hand in slot>

Starker places his left hand into the slot.  There is an empty space beyond the slot.  No noticeable effect occurs.

Starker puts his left hand out. He puts his left hand in and he shakes it all about. 

Based on Starkers feedback, Kragen moves around the Altar to see if the slot/s go through the entire slab.

They do not