Here is a three-quarter view of the end house on Doune Terrace. The front is faced with ashlar stone.
Ashlar is a building term. It is a building technique using blocks of stone that are cut back or tapered away from the front face so that there is room for the mortar between the blocks. The mortar is therefore in a wedge shape behind the front face.
From the front, the gap between the blocks is so small that it looks as though there is no mortar between the stones at all.
As you can imagine, it takes a lot of skilled work to cut a block of stone so that it tapers on all sides away from the front face. And skill costs money.
So, around the side of the building, the stone is like this: