Complex sentence: It was extended to cross the railway when this was built in the 1860s and was widened in the early 1960s, the upstream side comprising new masonry which blends in effectively with the older structure.
Split into simpler sentences: It was extended to cross the railway when this was built in the 1860s and was widened in the early 1960s. The upstream side has new masonry which blends in with the older structure.