Biological erosion of limestone coasts

In many places of the world such as the Straits of Dover, Gibraltar, and much of the Mediterranean, parts of Western Ireland, southern Sweden and in the Canadian Maritime Provinces, ancient limestone meets the sea because crustal movement and erosion have brought the two together. Along tropical coastlines, however, limestone is especially prevalent for another reason. Here, because of the growth of shelled organisms and perhaps chemical precipitation, there is an abundance of calcium carbonate. The absence of rivers along most arid and island coastlines means that rather pure deposits of lime can accumulate unadulterated by terrigenous weathering products. Within the last few hundred thousand years or so, the level of the sea has fluctuated several times by as much as 300 or 400 feet as glaciers grew to continental proportions and melted away. Both deposition and erosion have accompanied these oscillations of sea level and have left a complex record written in and...