sentences:  The historic town grew up on the southern bank of the River Liffey, a few kilometres upstream from the river's outfall into Dublin Bay.The original settlement was situated on a ridge overlooking a shallow ford in the river, which had probably been a regular crossing-point since earliest times.The bedrock underlying the city is calp limestone, a dark shaly sedimentary rock which was once quarried locally and whose mottled grey appearance can still be seen today in some of the city's oldest buildings.