Complex sentence: Shells left over from Timucua middens were burned by the barrelfull in open pits or kilns, then pounded into lime particles, mixed with water, sand, and whole oyster or clam shells, then poured into wooden foundations about high, and set to dry.
Split into simpler sentences: Shells left over from Timucua middens were burned by the barrelfull in open pits or kilns, then pounded into lime particles. The lime was mixed with water, sand, and whole oyster or clam shells, then poured into wooden foundations about high, and set to dry.