Marine: Marine sandstone is often characterized by its whitish of yellowish colour, and by the fact that it is often very texturally mature: consisting mostly of very rounded quarts grains. The constant reworking of the sediment by the tides and by longshore drift is what creates the purity of the sediment. The symmetrical nature of oscillation ripples, created by the tides, is a clue to sandstone being of a marine origin, as is the presence of marine gastropod, bivalve and brachiopod fossils. The Carboniferous at Corrie contains white sands that may be descibed as shallow marine sands which become deltaic and then fluvial, indicating delta progradation.

 Desert: Desert sands are deposited by the wind. These rocks are often very well sorted, consist mainly of quatrz, and are cross-bedded on very large scale, which helps to distinguish them from marine and fluvial sandstones. The absence of marine and freshwater fossils, as well as their red staining due to oxidation of the sediment, are further clues to a sandstone being of desert origins.

Aeolian sandstones outcrop on Arran at Corrie. Deposited during the Permian, when Britain was almostall desert, these rocks show excellent dune cross-bedding and are interbedded with conglomerates. The very homogenous nature of the Permian desert sansdtones makes them ideal for use in building as they are very easily workable. This is demonstrated by the photo of the "bath" with steps, cut into the desert sandstone on Corrie shore. This is'Dr McCredy's bath' - a long, deep bath carved out of sandstone on the foreshore at Corrie around 200 years ago. Dr McCredy, a resident of Corrie, presumably enjoyed sea-water baths - his permanent memorial on the foreshore at Corrie fills up as the tide comes in.

The workability of sandstone led many ancient people to use sandstone, for example in standing stones and in artifacts such as the one shown on the left, which was found on Arran.

River: River sandstones tend to be less sorted and not as mature as marine and desert sandstones. The variability in the supply of sediment, the type of river system and the fluctuation in energy of the system all make for different types of fluvial and delltaic sandstone deposits. A common rock type in rivers is conglomerate.

Rivers may be meandering, or braided. Sand tends to be deposited as point bars or in channels. The channels often cut into overbank fines and muds that accumulate on floodplains. Deltaic sandstones may contain fossil rootlets and fragments of woody material, as the point bars, levees and crevasse spays were often populated by early fern plants and lycopod trees.

The finest example of fluvial sandstones on Arran belong to the Carboniferous and can be seen exposed along the Corrie shore, especially near the Harbor and Ferry Rock. These rocks show fine unidirectional current ripples which are asymmetrical in nature, and often are succeeded by seat earth and/or coal, indicating a regressive phase with respect to sea level.

Follow this link to find out more about the commercial significance of sandstone, an important natural resource.