Googled Flat Bottom rail profiles and found this.
http://harmersteel.com/hs/wp-content...png?1398379987
That is of a similar dimension to the rail you found and indicates something around 20 lb / yard.
Network Rail currently uses 113 / yd or 56kg / metre.
With the general minimum weight of 98lb/yd being used over the last 60 years.
So your rail is of very lightweight and not designed for heavy traffic or for standard gauge vehicles.
Does anyone know what rail weight is used on 2ft gauge / 3ft gauge lines?
Lines of those sort of gauges would have been laid in the mid - late 1800's so any memory of post 1900 could be irrelevant.