Complex sentence: There has been limestone quarrying since the mid 1800s on the Penrhyn Bay side, centered on Porth Dyniewyd and served by its own narrow gauge railway, but quarrying ceased in 1936.
Split into simpler sentences: There has been limestone quarrying since the mid 1800s on the Penrhyn Bay side. It was centered on Porth Dyniewyd and served by its own narrow gauge railway, but quarrying ceased in 1936.