Ever wondered about the rocks and strata that make up the stunning Western Cape landscape? In his new book, Geological Adventures in the fairest Cape: unlocking the Secrets of its Scenery, John Rogers sheds invaluable light. By Joan Kruger

 

There is something irresistible about finding ‘geology’ together with ‘adventures’ and ‘secrets’ in one book title. At least you know that dense layers of intimidating data will not crush you to death.

Rogers aimed his book at those of us who are intrigued by strata (sub and super), improbable koppies on flat landscapes and quartz veins running along exposed ridges. Possessing only a smattering of geological knowledge, many of us often wish there were a geologist at hand who could explain what terrestrial forces – from volcanic eruptions to slow tectonic creep – created these geological marvels.

This is what this wonderful book does, and the beauty of it is that it will be equally useful to serious students of geology.

The premise of the amply illustrated Geological Adventures is to explore six routes heading across the Western Cape towards the Cape Peninsula and then to probe the Atlantic and False Bay coastlines.

A guide to exploring the Western Cape

To give you a taste of Rogers’s accessible writing style, here’s an example of how he guides you into Cape Town, should you approach it by air from the northeast:

“The best way to arrive in Cape Town is by air from Johannesburg. Ideally with a geological map of South Africa on one’s lap. During the second hour of the two-hour flight, one first flies across the barren Karoo landscape, underlain by river-deposited shales and sandstones of the vertebrate-rich Beaufort Group of the Karoo Supergroup. Several kilometres under the Karoo, out of sight for the moment, lies the older Cape Supergroup. The veld is crisscrossed by narrow dark ridges (dykes) of Karoo Dolerite, a black igneous rock that, while a molten magma, intruded the younger sedimentary rocks about 180 million years ago. This dolerite magma was en route upwards to a long-eroded ancient land-surface, as high above the Karoo landscape as our aeroplane, to erupt as highly fluid basaltic lava. A remnant of this lava caps the country of Lesotho to form the famous Drakensberg (Dragon Mountains). Little do the freezing Basotho shepherds know that their snow-capped peaks consist of basaltic lava that originally flowed at temperatures of 1 200oC – perhaps as hot as any dragon’s breath.”

You get the picture? You get the drama?

Rogers is as enthusiastic and, well, down to earth, when he takes you along on drives, whether by car or even, on Robben Island, by tourist bus. His interest isn’t limited to geological sites. There are few things that escape his notice, and he will draw your attention to the sites of shipwrecks, comment on gravestones or point out nesting colonies of kelp gulls at Wolfgat on the road to Muizenberg. This is not a geologist in lecturing mode, but an amiable conversationalist accompanying you.

Of rocks, pebbles, cobbles and boulders

Best of all is when you set out on foot and are able to touch the proof of Earth’s fascinating voyage through time and space. One such hike is when Rogers takes you along Tafelberg Road from the Lower Cable Station to Twelve O’Clock Hole and back, pointing out the weathered granite, which bears evidence of the wetter, warmer climate of 100 million years ago. More evidence of dramatic global climate change is the thick blanket of angular pebbles, cobbles and boulders of sandstone, on top of the granite. This, in turn, points to global cooling two million years ago when kilometres-thick ice sheets covered big swathes of the northern hemisphere, including Canada and most of Britain, and also left its mark on the southern tip of Africa.

Throughout the book there are references to books, articles and debates. Also to eyewitness accounts, which give the book a topical feel. A former pilot, in describing the sound of a debris flow [a type of landslide] that deposited enormous boulders near his home in Betty’s Bay, explains it as that of a “a Boeing that could not get going”.

The book is richly illustrated with photographs that help the reader identify geological features and events. This picture of Table Mountain taken from Tafelberg Road shows evidence of the landslide of August 2005. Pictures by John Rogers

Decoding geology for beginners

Rogers, a well-known researcher and lecturer, possesses a thorough knowledge of his subject matter, but he wears his learning lightly and is keen to engage and make knowledge accessible. There are amusing asides, such as advising the leaders of field trips to take care when shepherding a group across busy Victoria Road from the car park on the bend. He also informs you that he has two adult children, one family living on “Archaean granites near the Kruger National Park” and the other on the “Lebombo rhyolites of KwaZulu-Natal”.

Writing about geology is very much a ‘show-and-tell’ effort and the abundance of pictures, often annotated and always accompanied by detailed captions, makes the information come alive. Relative to the information needed, the visual material varies from aerial pictures to close-ups. GPS coordinates are supplied to the pictures, and speak of meticulous notes taken during innumerable field trips. A comprehensive glossary, bibliography and colour-coded maps add to the value of the book.

The pictures are annotated to point out geological features. This photo was taken along Clarence Drive, the main access route to Kogelberg Nature Reserve. The uphill side of the road shows evidence of a boulder beach deposited in the late Tertiary period. At this stage the sea level was 20m above the current shoreline.

 

Rogers succeeds in making the reader look at landscapes as well as at pebbles with new and informed eyes. Writing about False Bay, he applies a time scale to the profound variations in the sea level during the existence of our own species, Homo sapiens sapiens. And since you asked, that is about 100 000 years.

Initially, the scene would have been very similar to that of today, but 20 000 years ago the sea level dropped 120 m during a period of major global cooling. At this stage a long beach would have linked Cape Point to Cape Hangklip. Then, from 20 000 years to 6 000 years ago, as the continental ice sheets of the Northern Hemisphere melted, the low-stand coastline moved northward, steadily but surely to where it is now.

The book is true to its promise: it can turn a normal trip or hike in the “fairest Cape” into an exciting exploration of the secrets of the landscape.

Geological Adventures in the fairest Cape: unlocking the Secrets of its Scenery. Popular Geosciences Series 7. John Rogers. Council for Geoscience. 2018. R350.

Get a copy of Geological Adventures

Order from the author, [email protected], or purchase directly from the Council for Geoscience.

Council for Geoscience head office, 280 Pretoria Street, Silverton
Tel: +27 (0)12 841 1017

Council for Geoscience Western Cape, 3 Oos Street, Bellville
Tel: +27 (0)21 943 6700