The bridges of Prospect Park run the gamut from rustic to elaborate, but one phrase not usually used to describe them is technologically groundbreaking. However, the Cleft Ridge Span is just that. The bridge’s elaborate tile work isn’t composed of terra cotta or carved stone but cast concrete; a new advent at the time of the span’s construction. The idea to use cast concrete was an experiment of sorts. Originally, the plan was to use brick or granite, but park designers Olmsted and Vaux proposed a new mixture to save money….