What is limestone?

What is limestone?, originally uploaded by Mic2006.

What is limestone?

First and foremost limestone is a sedimentary rock. As seen in the picture above, it erodes and redeposits in fantastic and ornate ways.  Limestone is made of the skeletons of corals and tiny sea creatures, but it can also be made of calcium based chemical precipitates. The colors of limestone are many and varied. It is most typically a result of chemical impurities, and when subject to heat and pressure limestone meta-morphs to marble; a banded and crystalline rock that is seen in some Ontario caves as beautiful swirling bands. As is the case of the Silurian age Niagara Escarpment, when calcium is replaced in part by magnesium, dolostone forms, and although it is similar to limestone it reacts entirely differently to water.

Check out this amazing video on caves and karst landscapes. It speaks of how limestone is corroded, how sinkholes develop and what the impact of caves is upon geography – video on karst topography here.

The different types of limestone are many and varied, but two broad classification systems govern the names you will hear them by. The Folks system considers limestone upon the basis of the composition of its grains and interstitial material, while the Dunham classification is more focused upon the texture of the rock.

In relation to its cave forming potential, limestone in Ontario is situated in either the west of the province, deposited during the Devonian age and still as of yet hiding its caving potential beneath the thickly deposited glacial tills, or it it is found at the eastern edge of Ontario, at either edge of the lobe of the Canadian shield that juts southwards, down towards Kingston. Being situated at the outer edge of the former Michigan Basin, these eastern limestone’s are considered the most favorable in the province for the development of caves. The most notable cave forming limestone’s are those of the Bobcaygeon Formation a rock of the Ordovician age.

About 10% of all sedimentary rocks are classified as limestone. Other rocks that are commonly found inter-layered with limestone are sandstone, dolostone and shale. The presence of a shale layer is especially favorable to the development of caves. In our newly discovered cave – Wasteland Waterway we are expecting to come across a layer of the Rochester Shale soon. As shale is impermeable we expect it will change the nature of the system.

To read more about caves and limestone in Ontario check out my newly published book on caves,  Caving in Ontario; Exploring Buried Karst. In this book you will see mysterious tunnel systems that have developed in the limestone of the province. I also feature caves that have developed in marble and dolostone. There is a fantastic story of exploration that has remained somewhat unspoken of till now.