My great-grandfather was a chap called Jacob Rowlands. He was a guard on the Talyllyn railway. He had a brother called John (or Jonathan )Rowlands, who drove engines on the same railway. If you look at the 1901 census for Tywyn, you'll find both their details. I think the website is peter-davies.org/census files/towyn 1901. The address for John Rowlands is 34 , Frankwell street, and his brother (I think, because rowlands is not a rare name in Tywyn), lived at railway view.
I'd therefore extrapolate that your Great uncle is my great-grandfather's brother
how are you related to John/Jonathan Rowlands ?