This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol1", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
Bricks by themselves are not suitable for cornices of very great projection, especially for cornices of the Classic type, though in conjunction with stone they lend themselves very well for this purpose. Cornices should not project more than 9 inches when used without stone to give them strength. Fig. 146 shows a few such cornices
On the other hand, bricks lend themselves very well to cornices of the Gothic type, or to what are more correctly termed "Corbel tables," an illustration of which is given in Fig. 147. Cornices, like corbels and all other oversailing courses, of brickwork should be built of headers bedded in cement.