However, I found myself immediately corrected and was shown how the fabric had a very subtle nap to it which you could better feel than see. I was informed that this weave is called 'castor'. Having never heard of castor, I immediately looked it up. One reference stated that it is "a heavy, quilted all-wool face finished fabric, suitable for overcoats; it is heavier than kersey, but a little lighter than beaver." Another defined it as "heavy, all-wool fabric similar to broadcloth, but lighter in weight".
The trousers go with a matching frock coat, which judging by the way lapels are cut as one piece with the body of the coat, I would estimate as dating from 1918-1925 or so. The fabric is about 18 Oz weight but with a beautiful lush, almost velvety texture which recalls that of flannel. I have seen the faille and barathea weaves from the H Lesser books, but this was much more velvety and luxurious.
It occurred to me subsequently that amongst the other thing this could be might include a woolen broadcloth. This was once a standard woolen fabric for frock coats and dress suits. One reference defines it as:
"Fine wool, closely woven, napped and calendered fabric in plain or twill weave, usually twilled back. Better grades have gloss and a velvet feel".
If you look carefully at my scan you can see a diagonal twill pattern going through it which further distinguishes it from the satin weave of a faille. I looked again at the original and confirmed that the subtle but definite diagonal twill pattern going through it is real and not artefactual.
The more I think about it the more I am beginning to think this is classic woolen broadcloth, as it was the most basic fabric used for full dress, though castor seems to be a similar weave. Either way, never have I seen such a beautiful fabric in any swatch book today. Why on earth have mills abandoned making such niceties?