Clinker bricks

I imagine that these bricks in a local wall are clinker bricks.


I am indebted to Wikipedia for the following explanation.
 
Clinker bricks are partially vitrified. 
 
Clinker bricks are produced when wet clay bricks are exposed to excessive heat during the firing process,  sintering the surface of the brick and forming a shiny, dark-colored coating.  Clinker bricks have a blackened appearance, and they are often misshapen or split. Clinkers are so named for the metallic sound they make when struck together.
 
They make a great abstract pattern too.