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I recently came across this image regarding the Sheppard Subway Construction back then. It's my understanding that there are connecting tracks between line 1 and line 4. I believe there are ones that connect the tail tracks on line 4 with the southbound tracks south of Sheppard-Yonge station. I'm guessing that this trench here isn't the connecting tracks? Because the hole that currently sits on this site is much deeper than this.
Likewise with the Hullmark Centre across the street, would the little plaza be where the connecting tracks would be?