525 million year old Tapeats sand over and around  one billion year old quartzite

Taking geology classes gives one a whole new perspective on the landscape.  One begins to notice offsetting by faults, or intrusions.  On the South Kaibab I have walked past this rock hundreds of times.  Last weekend it was featured in a lecture about the Grand Canyon Supergroup, and I sat down and had lunch here today.

One billion years ago, the Shinumo Quartzite (or more accurately, the Shinumo meta-sandstone, see below) formed a cluster of islands in an advancing sea.  The Cambrian Sea, for such it was, surrounded these islands, often knocking pieces of Shinumo off the cliff and into the sea sand beneath.  Think the sea stacks on the Oregon Coast.

The Olympic Peninsula
 

As the trail winds down through the Supergroup on South Kaibab, one can see boulders of Tapeats with huge hunks of Shinumo lodged in the sandstone.  It almost looks as though they could be picked up and moved, but of course, they are part of the rock matrix.

Shinumo rocks which were knocked loose by wave action and stuck in beach sand.

This section of trail follows a block of Supergroup which was faulted down during the breakup of the continent of Rhodenia.  I am outlining a talk I will give in April about the history of geologists at the Grand Canyon.  While I was researching it occurred to me that the geologists who came out west: Newberry and Powell and Blackwelder, had studied geology in Europe or back east.  They had never seen rivers that could cut through mountains and plateaus.  They had never seen rocks that folded and bent in the scale seen around Mexican Hat.  This was a completely new paradigm for them.  A few of them suggested that the land had uplifted, but this was before plate tectonics, so all they could imagine was the land moving up and down via volcanic action.  This must have totally blown their minds.

Bill Nye says that when scientists find something they cannot explain, this is great!  This is how science and knowledge advance.  When new information becomes available, science incorporates it to explain old ideas.  When plate tectonics was first suggested, everyone said, great idea, but what is the mechanism?  Then during deep water exploration in the 1960's, scientists discovered lava pouring out in deep ocean trenches, pumping out acres of basalt which are pushing the oceanic plates apart.  Ah ha!  Here is the mechanism!  And tectonics were used to explain heretofore unexplained phenomena.

I have an old science book with a map of the world superimposed with dinosaur icons.  Since the same types of dinosaur fossils are found on different continents, this book explained,  the climate was the same sixty five million years ago in these disparate areas.  Well, it was, but because it was all one continent.

There is a lot I don't know about geology.  Of course, I know extremely educated geologists who, when I ask a question, will still say,"well, I'm not sure about that one."  Wayne Ranney says that one geologist is a blessing: two is an argument.

I once asked why a metamorphic rock (Shinumo Quartzite) can be layered between two sedimentary rocks (Dox Sandstone and Hakatai Shale) and was told that the sophistication of my question indicated my progress in understanding geology.  Wow!

The answer is that all the Supergroup was buried long enough that every layer underwent a bit of metamorphism.  And the layers should actually be described as meta-sandstone, meta-shale, etc.  But since most people are still at the Deposition Uplift Downcut Erosion level of geology, the interpretive signs won't change anytime soon.