Wednesday, May 29, 2013

Geology of Newfoundland - a book review

Geology is a big part of our kayaking experience.  The rocks in the cliffs we paddle by have a story to tell.  Therefore, I believe, some knowledge of the subject adds to the pleasure of the activity.

"Geology of Newfoundland" by Martha Hickman Hild is a field guide to 48 interesting sites in Newfoundland with an introduction to basic geologic concepts.

Each site is explained in terms of it history and setting with pictures and GPS co-ordinates.  I recently visited two sites at Manuals River to test the layout and explanations in the book.  It was also a good opportunity to use the waypoints feature in my GPS, which up to then I had not used.  So, I entered the two waypoints into the GPS and off I went to the ...

... first outcrop (outcrop meaning rock exposure) at Manuals River in Conception Bay South.

The knobby rocks by the water are layers of volcanic ash that were belched by volcanoes in the late Pre-Cambrian and later intruded by the magma that fed the very same volcanoes.  The directions provided in the book were very accurate and the provided picture ensured that even the armchair geologist could confirm for themselves they were in the right place.

The second site features sedimentary rocks that are dissected by a mafic dyke.  Geology, such a simple science in some ways, is full of complex nomenclature.  Mafic means "dark" as in made up of dark minerals.

The dyke runs diagonally from the middle bottom upwards to the right and bounded by the obvious straight lines on either side.

Some other geology enthusiast had been at the site recently and broke off some of the rock to verify it was dark.  The dyke (a rock called rhyolite) is related to the granite further downstream.  The rhyolite, cooled quicker than the granite, formed smaller crystals, making it look dark compared to the pink granite which crystalized slower at depth.

The co-ordinates provided (N47.51282, W52.94029) put me right on the outcrop and again the provided picture verified I was in the right place.

I was happy with the directions and explanations in the book.  As I was in the area I walked downstream and below the bridge over Manuals River to check out some of the geology which wasn't included in the book.

Here, water flows over Pre-Cambrian conglomerates that were deposited on top of the eroded granites.  In a nutshell, the volcanoes and rocks overlaying the granite body that lay several kilometers underground were eroded, exposing the granite, after which sea levels rose depositing various size cobbles much like those on any beach.

This is a close-up of the conglomerate.  The cobbles are rounded indicating they were either transported over considerable distances or were worked by waves along a shoreline.

I continued down, following the river, until the rocks became black slates.  These rocks were deposited in deeper waters in the early Cambrian period just after 542 million years ago.  Some of the sedimentary beds contain trilobite fossils which places the rocks firmly in the Cambrian.

We have a kayak camping trip planned for New World Island.  The book lists several sites in the New World Island area so, based on these explanations, I expect they will be easy to find.

I believe anyone with even a rudimentary knowledge of geology would find this book useful.  Its an excellent buy for the $34.95 it costs.

No comments:

Post a Comment