Over 340 million years ago the Torquay limestone was formed by the deposition (laying, down) of dead coral reef material. About 270 million years ago it was affected, along with other rocks, by mountain-building processes (folding, faulting, earthquakes + volcanoes). Many faults (cracks + joints) were formed which later allowed water to pass freely through the limestone.
About 2 million years ago, the limestone became exposed at the ground surface when overlying rocks were finally removed. The cracks were steadily widened and deepened by acidic surface water which reacted with the limestone (dissolution), dissolving it and carrying it away. Rainwater becomes slightly acidic as it picks up carbon dioxide (C02) from the atmosphere. It picks up further quantities of C02 from decaying plant material (humus) as it passes through the soil layers.
Gradually the first caves began to form. As running water entered the limestone, mud and grit were also brought in and, where the water entered with force, erosion (gradual wearing away of the surface of the rock) also occurred. At first the caves were completely filled with water, often under great pressure, so that erosion of the roof as well as the sides and floors of the caves took place.
The caves gradually grew larger by dissolution and erosion, and by the fall of large blocks from the roof, especially when the water levels were falling and air spaces occurred.
By about 500,000 years ago the Kents Cavern caves had almost reached their present size and large flows of water passed through the limestone in fissures below the level of the present pathways.
Eventually some of the material carried into the caves by the water was deposited (left behind) on the floor and sides of the passages. Having reacted with the limestone the water seeping into the cave contained not only calcium but also a great deal of dissolved C02, much more than the air within the caves. In contact with the cave air C02 was released from the water, causing calcite (calcium carbonate) to be deposited in stalagmite (on the floor) and stalactite (on the ceiling) formations.
During the last 500,000 years Britain's climate has changed many times from being as warm or warmer than today (interglacials) to very cold (glacials). The stalagmite and stalactite formations only form in warm periods, when vegetation and soil cover the lands' surface. In the cold periods the caves were filled with clayey, stoney material called Breccia and cave earth. This material was produced by much freezing and thawing on the lands' surface and entered the caves through the entrances and large fissures.
During parts of some of these cold periods the caves were occupied by animals, and even by human beings. Many fossils and stone tools made by Man have been found and a lot of these can today be seen in Torquay Museum.
Throughout these periods of warm and cold, further dissolution, erosion and deposition occurred in the caves, producing and partly destroying many layers of sediment and stalagmite.
Since 1824 geologists and archaeologists have been trying to understand the sequence of sediments and work out when animals and men occupied the caves.
The first excavations merely broke the surface layer and exposed remains in the cave earth (material deposited during the last cold period).
Subsequent excavations in the 1860's went much further and revealed the presence of a second stalagmite floor, dating back more than 350,000 years (see 7). Twentieth century research has opened up even older deposits and the earliest sediments and fossils may now appear to be over a half million years old.