Striation directions

the direction (compass) of one of many thin lines or scratches, generally parallel, incised on a rock by some geological agent such as a glacier or stream. See glacial pavement.



laminated calcareous sedimentary formations produced by lime-secreting cyanobacteria. Living stromatolites are in the shape of stony cushions or massive columns. Fossilized stromatolites (silicified) dating well back to the Precambrian are found in the Gunflint Chert of Lake Superior, in cherts of Africa and Australia, and in calcareous sediments.



the movement of one crustal plate under another so that the descending plate is "consumed".



a collection of many smaller continents to form one giant landmass.



a sedimentary rock formed by the compaction and cementation of till. Till is generally not layered and deposited directly by glacial ice. It is poorly sorted with a wide range of grain sizes from clay to boulders. Clasts are usually angular because they have undergone little or no water transport.



the carrying away (transportation) of sediment by the agents of waves, wind, streams and glaciers. See erosion.


unconsolidated sediments

sediments which have not yet been compacted and cemented to form rock.



process by which regions of the Earth's crust is raised above sea-level. This process is most commonly associated with rifting and collision of continental crust.



destructive natural processes by which rocks are altered with little or no transport of the fragmented or altered material. Mechanical weathering occurs with the freezing of confined water and the alternate expansion and contraction due to temperature changes. Chemical weathering produces new minerals. The main chemical reactions are oxidation, hydration and solution.


Witwatersrand rocks

rocks belonging to the 3000 million year old Witwatersrand Supergroup which outcrop around Johannesburg and south into the Free State. The Witwatersrand rocks are significant in that more than half of all the gold produced has been extracted from these rocks.



silicate mineral, ZrSiO4, an important ore for zirconium, hafnium and thorium; some varieties are used as gemstones. Zircon is a typical accessory mineral of acidic igneous rocks and their metamorphic derivatives. It also occurs as a detrital mineral.


Sources Consulted:
Farndon, J. (1998). Concise Encyclopedia Earth, Dorling Kindersley, Great Britain, 192.
Lapidus, D.F. (1987) Collins Dictionary of Geology, Winstanley, I. (Ed.), HarperCollins, Great Britain, 565pp.

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