The photograph above is, as stated, from the Lawrence Collection in the National Library and dates to around 1890. It seems that that crane photobombing the photo was very much a permanent fixture on the pierside, probably used for dredging and/or loading/unloading.
I don't know what the technical term is, but the cast-iron lighthouse has a hood - or is it a balaclava? - controlling the direction of the beam. Painted white, it bears a resemblance to both the ill-fated Bray lighthouse and also, and especially, the Sherkin Island lighthouse, both constructed towards the end of the 1800s. The latter two lights, though, have a balcony, which Buncrana lacked at the time.