The tree of happiness flowers and fruits most abundantly for the creative man
I live atop the Berea Ridge, Durban, with almost 360 degree views of the Durban district. One can see the Indian Ocean, the Bay of Natal the Bluff, the Berea Ridge stretching to my left and right and fine views inland towards Queensborough and Westville, and in the distance the Inanda Plateau and Etafuleni. Residing in an area generally quickens an interest in the local geology. I am sure it is true for those who live near Table Mountain in the Cape, or those who live along the fiords of Norway or on the islands of the Scottish Outer Hebrides.
The geological formation of the Bay of Natal, the Bluff and the Berea Ridge is an exceedingly difficult subject to understand. Having no education in this strata of knowledge I have stumbled up the Cretaceous dunes and down the Pliocene ridges. My conclusion – no matter how clever the geologist, no matter how erudite the lecturer, no matter how well written the book – if I cannot visualize the events of hundreds of thousands of years, I am drowning in a coastal inundation. It simply must be my visual disposition.
My solution – has been to draw charts and pictures of the events, sequentially and chronologically, in the hope of gaining a better understanding of the subject. I trust that when I walk along Ridge Road, or idle along the Ocean Promenade, I will have a fuller appreciation of the land that lies beneath my feet.
(above) The land of Natal and Zululand has seen many inundations and denudations by the Indian Ocean. This as a result of the rising and dropping of the ocean surface, but also as a result of the landmass having a tendency to tilt like a playground sew-saw. first one way then another. The Indian Ocean’s waves have crashed upon many shorelines, many – much further inland than the present one; and many much further out than today. This state of constant flux has happened for millions of years, and no doubt, will continue for many millions of years more. Each tilt, every shoreline movement – adds new geology while scrambling or burying the previous. Add to this the erosive effects of rainfall, ice, wind and rivers, not forgetting their ability to deposit what they have stripped in other far off locations. Further more – forces deep within the earth can sheer rock beds, thrusting up some sections and dragging down others along fault lines. These forces can also force molten larva up and through the earth’s crust to the surface where it can flow like water, covering thousands of kilometres of land to eventually harden into rock, like the basalt beds of the Drakensberg Mountains. Lastly – there is the process known as ‘Continental Drift’ where vast chunks of land pull apart and ride like rafts across the surface of the earth to new locations. No wonder this topic has taxed my brains and addled my thinking.
All sound buildings need good foundations, and this posting is no different, so I am going to build this story on the firm crust of South Africa’s foundational land blocks. It should be remembered that South Africa at this point in time was a part of the greater Gondwanaland landmass.
(below) Oldest of these blocks is the ‘Kaapvaal Craton‘ and ‘Natal Metamorphic Province‘. Two land masses or blocks, side by side, upon which all subsequent geology was built and derived. These masses are 3500 to 3000 million years old. Of interest – the Kaapvaal Craton is among the very few surviving and pristine crusts to be found anywhere on the earth. This crust is composed of basalt with granite intrusions.
(above) Approximately 1000 million years ago, subduction forces beneath the earth’s crust pushed the ‘Natal Metamorphic Province’ block into collision with the southern edge of the ‘Kaapvaal Craton’ block, forcing super heated rock upward into a mountain range that stretched many thousands of kilometres. This range was gradually eroded away to leave hard granite and gneiss deposits. An example of these granite remnants is the feature called “Old Baldy’ in the Valley of a Thousand Hills, just inland from Durban..
(below) This was followed up by the ‘Natal Group Sandstones‘ (Table Mountain Sandstone) layer. This first sedimentary layer from 490 million years ago, is the result of rain and river erosion of earlier rocks in the highlands to the north east. The eroded sands were deposited atop the remaining Kaapvaal Craton and Natal Metamorphic Province basement. One can see these sandstone layers along the inner slopes of the Kranskloof and Oribi Gorges.
(below) 300 million years ago, when Southern Africa was still part of the greater Gondwanaland landmass, it was situated much nearer to the South Pole, and much of the land was covered in thick glaciers of snow and ice. These glaciers moved across the land in a south westerly direction, scouring the underlying bedrock and carrying within the glacier mud, pebbles and boulders. As these ice sheets retreated and melted they dropped their load of fine mud, boulders and pebbles into thick beds that hardened over time into the fine-grained blue-grey conglomerate called ‘Dwyka Tillite‘, These deposits can be seen near Durban where they have been quarried for a 150 years for aggregate and building material. (Umgeni Quarries)
(below) A sample of Dwyka Tillite with a crystalline inclusion from a revetment in my garden.
Then during the Permian – Gondwanaland moved closer to the equator. South Africa, at the heart of this landmass was covered by a large warm inland sea as part of the Karoo Basin. Thick silt and clay beds built up interspersed with the vegetative remains of swamp plants. These sediments hardened into Ecca Shale and are darkly-coloured from their carboniferous plant content. These shales break down quickly and easily when exposed to erosive agents. One can see these beds in Cato Manor, just inland from the Berea Dune, where they constitute unstable hillsides unsuitable for the building of homes.
During the Pliocene Period, approximately 5 million years ago, the sea level rose once again (as they had in earlier epochs) flooding over the Natal and Zululand plains, covering previous deposits and driving the shoreline well inland. As in previous inundations and marine depositions, the sea deposited beds of softer, lime-rich sand across the plain that hardened into vast beds of sandstone.
Towards the end of the Pliocene Period, the sea retreated in stages, and the previously laid-down beds of sandstone were exposed to weathering. These softer, friable rocks broke down quicker into loose sands than did earlier deposited rock beds like the Natal Group (Table Mountain Sandstone) and bands of Dwyka Tillite (a glacial sedimentary rock). This eroded sand was washed down the many streams and rivers into the ocean where wave and tide deposited the sand along the shoreline. During stages when the shoreline was relatively stationary, sea and wave action cut notches and cliffs into the coastal plain, and where the shoreline lingered, the loose sand piled up under wind action forming large dunes that ran parallel to the shoreline.
(above) During the Cenozoic, following one of the oscillations of the KwaZulu Natal landmass, the coastal plain was raised, and the shoreline receded to a position approximately where Umbilo and Umgeni Roads in the city of Durban are today. The shoreline lingered long enough to cut cliffs into the raised land composed of earlier Pliocene marine beds. Then winds began the gradual task of piling up a huge dune along this cliff, an impressive 65 metres of beach sand atop the rock bed of Natal Group, and Dwyka Tillite, Ecca Shale and Pliocene Marine that was at its highest 75 metres above the sea level. This created the Berea Dune/Ridge, a full 140 metres above sea level. From atop the modern Berea, this elevation is what affords residents fine views of the Indian Ocean, City, Bay and Bluff. Looking landward, the valley descends at approximately 30 degrees into a wide valley with its lowest reach approximately 1 kilometre away where the Umkumbaan River (a tributary of the Umbilo River) flows southwards. From this point the land rises moderately towards the modern suburbs of Berea West, Westville and Queensborough and the land is composed mostly of Ecca Shale. The Berea Dune runs from south of Durban all the way up to Mtunzini and at intervals well beyond. Just beyond Isipingo, it combines with the later Wentworth Dune, from where it runs in intervals further south.
The many rivers that flow eastwards towards the sea carried sand and silt down to the coast (as they do today). This erosion was increased when the landmass tilted to a steeper incline about 20 000 years ago. It is this tilting that resulted in rivers deeply eroding their courses into deep gorges inland from Durban, gorges like those at the Palmiet Nature Reserve and at the Krantzkloof Nature Reserve. It also resulted in the sea level dropping a full 120 metres below the present.
The rivers of Natal carry an abundance of sand down to the coast where the northerly littoral drift distributes the sand along the coast in a series of fine beaches. This sand is continually thrown-up onto the shoreline by wave and current action, where strong winds blow the finer sand inland where it piles up to form coastal forest dunes. Vegetation (like the kind found on the seaward side of the Bluff) stabilises the sand, allowing for the constant raising of the dune over many hundreds and thousands of years. The vegetation keeps pace with the sand deposition. On the Zululand coast some of these dunes are a full 150 metres high, rising precipitously from the sea at a gradient in excess of the holding capacity of fine sand, thanks to the anchoring affect of the vegetation.
The Berea Dune, of fine sand, blown inland from the shoreline, built up over many thousands of years to form the Berea Ridge of today, the foundation to the homes of may Durbanites since the 1850’s. These sands were originally white and calcareous and derived from earlier eroded Pliocene marine beds; a proportion of feldspar, and grains of silica and clay eroded from inland granite and Natal Group Sandstone, brought down by rivers like the Umgeni.
Many thousands of years of tropical weathering slowly converted a percentage of the feldspar to kaolin clay. The lime content in the sand (from the marine shell components) was leached-out, and iron-bearing minerals in the sands oxidised to be converted to red hematite and goethite, staining all the sand grains red, hence the Berea Red. Residents on the Berea today will be aware of the clay-like component to their garden soils when wet soil clogs the treads of their gardening shoes. The staining affect of the red soil on clothes will be all too evident to mothers of young children whose charges come in from the playground.
(above) In this illustrative photograph from Malacca Road, Durban, showing a cut-through of the the Berea Dune that in this location lies atop a bed of dark foundational Ecca Shale. Note that above the shale is a layer of lighter basal conglomerate sediment containing marine sand and many round sandstone clasts and pebbles. This the result of the shoreline having been situated near here and the waves having pummeled and eroded platforms and cliffs into the beds of Natal Group Sandstone (Table Mountain Sandstone). Along these platforms the sea deposited conglomerate beds of sand, boulders and pebbles, eroded by the sea or brought down by rivers from inland. As the sea retreated, onshore winds blew fine marine sand and seashell fragments from the beaches inland where it accumulated along this conglomerate band to form the Berea Dune. Lower layers of this fine dune sand is visible in this image as the white deposit. This sand has been leached by rain water. Above this layer is an accumulation of the typical and well-known red Berea dune sand.
(below) As illustrated below – in contrast to the dune sands lying on top of Ecca Shale, other sections of the Berea Dune lie atop beds of Dwyka Tillite. This can be observed at Umgeni Quarries, where the Umgeni River has cut a course through the Berea Dune and the Dwyka Tillite on its path to the sea. See an earlier posting on this blog regarding Dwyka Tillite – https://grahamlesliemccallum.wordpress.com/2014/05/31/dwyka-tillite/
(below) A photograph of an excavation on the Berea into the bank showing the oxidised Berea Red. The lighter band in the middle of the bank is the original line of the hillside. Below this band is virgin ground and above compacted Berea Red spoil.
(below) a turn of the century photograph of the Berea peppered with the residences of early Durbanites. Emmanuel Cathedral and the Grey Street Mosque is visible in the foreground.
(below) A photographic view from my home looking west from atop the Berea Ridge, looking inland towards the Pavilion Shopping Mall. The ridge in the middle ground is a finger of the Berea Dune.
(below) A scenic photograph of the Coastal Forest Dunes at Sodwana on the Zululand coast. (Courtesy – Photographer Carlos de Resende). This remarkable image records the height and dynamic nature of these South African dunes and the importance of the stabilising effects of the dune forest and vegetation.
(above) The process of dune building is repeated every time that the sea retreats to a position, which results in several parallel dunes separated by valleys. By the end of the Pliocene the shoreline had receded beyond the Berea Dune to a position where again it paused long enough to pile-up marine sand in what is today known as the Wentworth/Bluff Dune. Named after the pioneer farm located to the south of the Bluff. This dune is piled up against the Berea Dune at Isipingo from where it runs south in combination. From the tip of the present Bluff it piled-up in a much more north-easterly direction than does the extent north-north-east direction of the Berea Dune. This run of the Wentworth Dune is now drowned when the Indian Ocean inundated the much wider and flatter Zululand Coastal Plain.
Lower levels of old dunes of wind-blown sand can undergo a process of lithification (rock forming) which is a result of carbonate excrescence from marine mollusc shells. Sand particles become welded to one another to form coastal limestone, known as Eolianite. It is these eolianite remnants of the Wentworth Dune that compose much of the Aliwal Shoal, as well as the base of the ‘Bluff’ that protects the present Bay of Natal.
This eolianite sandstone was quarried at the base to the Bluff in 1853 to 1854 by John Milne to construct the Milne Breakwater to the mouth of the Bay of Natal. This stone was quarried at the headland to the Bluff, just opposite the Point. Milne in his harbour report for 1852 records the following… “there is a narrow beach of rock or a crust of indurated sand”. He noted that this sandstone was highly calcareous with fossil shells and fairly friable. Cave Rock (see my posting) situated at the headland to the Bluff was composed of this material. Milne had a railway built to convey the quarried stone around the Bluff to be ferried across the harbour mouth to the tip of the sandy dune called the Point. Ox-drawn carts conveyed the rock along the rail. (below)
(below) A drawing by Frederick Mackie executed in 1855 of Milne’s Breakwater.
(below) Evidence of the quarrying on the Bluff headland is evident in this early photograph taken from Milne’s Breakwater. Cave Rock can be seen on the far left of this image.
The recession of the sea and shoreline continued until the end of the Pliocene epoch, when the sea returned very close to its present position. Rising seas inundated and eroded almost all of the Wentworth Dune. Remnants of this feature are the Aliwal Shoal off the coast of Natal near Umkomaas, the Protea Shoal and the lower eolianite courses of the Bluff.
(below) A topographical map of the Aliwal Shoal. Courtesy of John Easton http://www.fishtec.co.za/index.htm
Where the city of Durban lies today the rising seas broached the shoreline where the Umgeni and Umbilo rivers transected the Wentworth Dune, flooding the valley between this dune and that of the Berea Ridge. Stretching from Umbogintwini in the south to approximately two kilometres north of the present mouth of the Umgeni River, a distance of 25 kilometres. This body of water must have been an imposing sight to behold. The northern stretch of the Wentworth Dune beyond the ‘Bluff’ was eroded and drowned.
(above) The inundation of the coast resulted in many of the Natal and Zululand rivers forming lagoons at their mouths, especially where the deposition of sand by the sea along the new shoreline blocked river mouths causing the rivers to be temporarily trapped behind these new spits of sand called ‘beach bars’. As today, heavy downpours in the hinterland can rapidly swell rivers and force exits to the sea through these sand bars. A case in point is the mouth to the Umgeni River that in more modern times formed the well known known ‘Blue Lagoon’ where the flow of the river is often blocked behind a bar of marine and river sand.
(below) A photograph of Blue Lagoon taken in the early 1900’s.
(above) Sea, river and wind action in league with coastal vegetation created a sand bar that extended in a southerly direction from just north of the present mouth of the Umgeni River. The majority of this sand is as a result of the littoral current that hugs the coast line and sweeps around the Bluff headland, offloading vast quantities of sand onto the Annabella Bank and beach bar. This beach bar (in fact a young sand dune in the making) almost meets up with the tip of the projecting Bluff (the present mouth of the Bay). The course of the Umgeni River was diverted south. When the pioneering settlers arrived in the 1820’s they named this young dune/ beach bar – the ‘Point’ or ‘Sandy Point’.
An informative painting from the 1850’s by artist George French Angus looking south and down from the heights of the Berea from the rough track that led inland, towards the nascent town of Durban, the sandy Point to the left that separated the bay from the Indian Ocean, the expanse of the Bay of Natal with Salisbury, Ogle and Farewell Islands, and the Bluff and Wentworth Dune in the far distance.
Emptying their waters into the greater lagoon (Bay of Natal) from the south were the Umbilo, Unhlatuzana and the Umbogintwini Rivers. These rivers carried sand from the hinterland and deposited this load into the lagoon, slowly silting up the body of water from the south. The Umgeni River emptied into the lagoon from the north, forming a fanned delta. At some point the land of the delta rose approximately 6 metres allowing this area to partially drain. This rise stopped the flow of the Umgeni River into the bay and the river broke through the beach bar to empty directly into the ocean. It is evident though that when the river came down in flood that it would sweep across the plain and empty into the bay. This happened in 1856 when after torrential rains inland, the river came down in flood and swept along its former route into the bay and damaging much of early Durban.
When the pioneers arrived in the 1820’s two marshes were located in this area, namely the Western and Eastern Vlei (Marsh). The Western Vlei drained into the bay via Mullet Creek and the Eastern Vlei via Cato’s Creek. Early Mariners who visited the bay in earlier centuries would draw water from these water sources, especially Buffalo Spring located today at Old Well Court off Smith Street. It was this delta’s silt and sand load that creating the plain upon which the city of Durban is built today. Excavations for the foundations of high rise building in the city reveal these former delta river courses. The water table lies very close to the surface as well. Where the Nedbank is situated today in Smith Street the water table is only 2.6 metres below ground level. At the Old Durban Station it lies at a depth of 2.84 metres, and at the Old Fort which lay adjacent to the Western Vlei, a mere 1.3 metres. One can understand why the water reached the surface at Buffalo Spring.
Just above the Western Vlei are the footholds of the Berea Ridge, and it is from this area that the vlei was fed with fresh water. This source, just below the Botanic Gardens, was exploited in early Durban days to provide a burgeoning town with potable water. Pioneer H. W. Currie was responsible for locating this critical water source, hence the name given to the area today, namely ‘Currie’s Fountain’. Rainwater falling on the Berea Dune, percolates through the fine sands and is carried laterally to the east above and between layers of semi-impermeable sandy-clay and impeamable clay that lie above layers of Ecca Shale and Dwyka Tillite. A fault zone between these two formations is located here that channels and concentrates the water flow. If one visits the lower grounds of the Durban University of Technology where their plant nursery is located, one can witness this artesian water flowing from the earth.
(above) The precise location where Currie sited his well is not known. It is believed to lie below the reclaimed land where the Currie’s Fountain Stadium is today, or the field between the stadium and the lower Botanic Gardens. Evident in the photograph, and within several hundred metres of the stadium, water flows unhindered to the surface. Clear and drinkable perennial artesian water spills out of a pipe located in the grounds of the Durban University of Technology. This spring is located some 30 metres from intersection of Mansfield Road and Winterton Walk. Today the water from Curries Fountain flows underground in pipes in a southerly direction along Centenary Road where it combines with the run that drains the Western Vlei where the Greyville Racecourse and the Royal Durban Golf Club are today. Further south the drain runs along Brook Road, dispensing its run into the canal at Maydon Road and along Canal Road to the Bay of Natal. The late Ecologist and Academic ‘Cecil James Ward’ (Roddy Ward) informed me that in earlier years, this water course was known as ‘Mullet Creek’. He allowed me to photograph an old watercolour painting in his possession of the location where Mullet Creek empties into the Bay.
(below) Mullet Creek.
(below) A painting of the Bay of Natal taken from the Berean Ridge by Captain Robert Jones Garden (of the 45th Regiment) 1849. Mullet Creek is visible in the middle of this image.
Of interest – on the eastern boundary of the vlei (marsh) Captain Smith ordered the sinking of a well to supply the needs of the British soldiers at the fort (Old Fort).
(below) Old Fort Well.
Drillings taken of the sediments around the present Bay of Natal (Durban Harbour) record that these sediments are a full 21 metres thick. The base is composed of a layer of black fine-grained bog iron ore that is 24 950 years old, followed by sediments of grit and sand, including a band of black clay between 9 and 12 metres deep that is 4800 years old and indicates an earlier salt march.
(below) Aerial photograph looking towards the headland of the Bluff with the Indian Ocean to the left and the Point to the right. The Bay of Natal and its entrance is in the middle of the image.
(above) A drawing of the Point looking south from Cato’s Creek over the hummocks of the Point dune towards the Bluff and its signalling mast, 1850.
(below) A photograph of the Point taken from the heights of the Bluff (Wentworth Dune) showing the young sand dunes anchored by vegetation, the Bay of Natal, the Berea Ridge in the far distance, and the mouth to the Bay in the foreground.
Graham Leslie McCallum