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Unusual Landforms
Unusual landforms are characteristic of a karstic landscape. The limestone pavement divides into blocks, called clints, and deep fissures, called grikes. Erosion gradually widens and deepens the grikes, to the depth of a meter or more. The most famous area of karstic landscape is the Burren District of northwest County Clare in Ireland. Limestone cliffs often appear at the edge of an area of carboniferous limestone. The cliffs are almost vertical with many vertical cracks, called joints.
Swallow Holes and Underground Drainage
Carboniferous limestone is pervious rock, rock that allows water to pass through small cracks and joints. In some areas covered by the grits and shales of younger, upper (layers), carboniferous millstone, streams reach the limestone boundary and disappear into "swallow" holes that drain underground. A well-known swallow hole is in Burren, at Poulnagollum. In the lowlands east of Burren, water drains underground from the Gort area, to near Kinvana, where it bubbles to the surface.
Cave Systems, Gorges and Dolines
Over time, the underground drainage creates large cave systems or, in some cases, the collapse of an area of limestone pavement. The caves, or caverns, contain stalactites, stalagmites and pillars of lime deposits. Some of the caves are accessible to tourists and range in length from 10 to 15 meters. Gorges form when a large underground cavern with a river running through it collapses. Dolines are small underground caverns that collapse, leaving an indentation in the surface of the land.
Transient Lakes
Transient lakes, called turloughs, occur in carboniferous limestone lowlands. They appear or disappear as the water table rises and falls.
Dry Valleys
During glacial times, the ground froze, preventing water from draining through the limestone. Rivers flowed on the top surface of the carboniferous limestone and eroded the stone to form deep valleys.