Keith, that's an interesting perspective. I had always chalked it up to a requirement for public buildings to appear impressive, and almost intimidating (like old churches as well), but you're right in that there was a time frame where we had a number of stone masons who had come from Europe to work on the Shubenacadie Canal. I have read where stone buildings were more doable back then because of the excess labour force who had those skills (especially after the canal project failed), plus materials were still readily available (and probably helped to keep the quarries in business). That said, I don't believe that similar stone buildings were unique to Halifax, though.
The architecture is quite impressive, especially for a small school, IMHO. Hate to say it, but to my eye most newer public buildings look like crap in comparison (highly opinionated as it is)...
Also on the NS archives site is what appears to be the same photo with notes on it:
Source
The notes at the bottom say it was replaced by a new building in 1951 and demolished in 1955.
Also of interest are the separate entrances for girls and boys. I never really understood this, and thought of it as an extension of the Catholic school model, but my elementary school (Greenvale) carried on this practice right into the 1970s. Girls and boys entered through opposite sides of the school, and recess and lunch breaks were spent outside on separate sides of the school. If you tried to go to the other side, the on-duty teacher would stop you from doing so. Oddly enough, once you got back inside, boys and girls mixed as usual. I never really understood this practice, and thankfully it disappeared shortly afterwards.