The bus came to a stop after a steep climb up the Munroe Drive, which starts in Lower Houghton and ends up in Upper Houghton.
From what I could understand, 374 million years ago, a bit before my time, two land masses called 'Cratans' crashed into each other in the area where present day Hawaii is. The one cratan ended up subducted under the other (it got caught underneath and then sloped up as a result - hope you can see this picture in your head!) Over time, with moving about and expanding and whatnot, they ended up right here! This area is called the Witwatersrand (white waters ridge) basin. There is some controversy as to how the name 'Witwatersrand' came to be, the most popular theory is that from far off the ridge shimmered and looked like water.
It was formed 360 million years ago. And it is massive. Now, way back in those days there was no atmosphere and this basin was a sea. Electrical storms (something that hasn't changed!) caused massive erosion over time, and caused the sea to fill with sediment to a depth of 8kms (almost 5 miles) - that is higher than Mount Everest! And that was the end of the sea. Pity, because it now takes 6 hours of driving to get to the sea....
Anyway, back to the ridge we were standing on... an interesting fact: when it rains, any water that runs off over the edge here, into Lower Houghton...eventually ends up in the Indian Ocean. Any water that runs off down the other side (which I'll show you soon) ends up in the Atlantic Ocean! Fascinating, Fi can't believe she had never heard that before. She needs to go on more of these tours, I think!
Another thing: GOLD! Gold forms in rock strata. The strata that Johannesburg gold formed in, is at a terribly steep angle as it formed in the 'cratan' that ended up tilted up at the funny angle under the other one. There was such a nice piece of exposed rock on the way down the other side that showed you how steep this strata is but Fi wasn't quick enough to take a photo, sorry.
This steep angle makes mining for gold very difficult and that is also the reason the mines here are so very, very deep.
Right, back on the bus....
