According toG.T. Dodwell a Norwich Convention was called in the 1890s from which the official 'type' standard emerged. The Norwich is a 'cobby' and thickset bird of about 6.5" length with a thick neck and a massive head. The birds are colour fed to produce a deep and rich orange tone.
Cayenne-fed Norwiches from the 1860s by Ludlow
Sadly, as with so many varieties, the craze for bigger and bigger birds, with denser and denser feather, has produced a modern bird that is a very poor reflection of the classic Norwich.