I heard a different origin to the Black & Tan than what is on Wiki. The version I heard said the B&T originated during the Unionist/nationalist divide in Ireland. As you know, the nationalists wanted Ireland to be sovereign whereas the unionists wanted it to be part of the UK. There was also a strong religious divide between the protestant (English) and Catholic (Irish). The drink was created by the nationalist Irish as a joke of those Irish who were unionists, as they considered them traitors or something to that affect.
The Black & Tan has the Irish Beer on top and the English beer below, meaning to suggest that although the unionist Irish may appear Irish on the surface (Irish beer on top), they're really Englishmen deep down (English beer on the bottom). It's meant to be an insult or a joke drink. That's the way I heard it, and I'm not sure if that's 100% correct or fake, but there you go.
I'm not sure which is supposed to be on top. All I know (speaking from experience) is that you should pour the Guinness VERY slowly on to the spoon. It also helps to have the special spoon made specifically for this drink.
The Black & Tan has the Irish Beer on top and the English beer below, meaning to suggest that although the unionist Irish may appear Irish on the surface (Irish beer on top), they're really Englishmen deep down (English beer on the bottom). It's meant to be an insult or a joke drink. That's the way I heard it, and I'm not sure if that's 100% correct or fake, but there you go.