Seven Days Work EarthCache
Hidden : 9/20/2010
Difficulty:
4.5 out of 5
Terrain:
4.5 out of 5

Size: Size: other (other)

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Geocache Description:

This earthcache tells the tales of how the Grand Manan Island cliffs that you see first see from the ferry were formed and named.

Seven Days Work is a perpendicular rock formation showing what appears to be seven strata of rock piled to a height of over 200 feet. Grand Mana is comprised of two great and widely differing sections, dividing the Island almost from end to end. Dr. Abraham Gesner the provinical geologist in his 1839 account titled, “First Report of the Geological Survey of New Brunswick” called designated the western section as “trap rock” (of volcanic origin) and the eastern as schistose (sedimentary) rock. The western 2/3 of the island contains this trap rock, thick lava flows of Early Mesozoic age, which are little changed from when they cooled in the beginning of the Jurassic Period. They are part of the enormous “flood basalt” that underlies most of the Bay of Fundy, and which erupted 200 million years ago.

The Grand Manan Basalt is divided into three sections, or members, something like a cake with layers of frosting in the middle. At the bottom is the Dark Harbour member, a single massive flow, which forms cliffs up to 100 meters high along much of the western shoreline. As it slowly cooled in a huge lava lake, vertical columns formed from bottom to top. The basalt columns are well developed and appear to be continuous, i.e. not interrupted by flow boundaries or horizontal segregations such as have been observed in other basins. Above these columns, the Seven Days Work member, which is comprised of 12 to 14 lava flows each a few meters thick. The flows contain a variety of attractive minerals along the famous cliffs of their given name. The upper member is called Ashburton Head, where you can see another thick pile of massive lava something like the bottom member. The upper members of the Grand Manan Basalt have apparently been removed by erosion over much of the island. Beneath the basalt are thick formations of Triassic siltstone and sandstone up to two kilometers deep.

While from the ferry it will appear that there are seven layers there are between 12 and 14 layer each representing new lava flows. The view from the water is where the formation gets its name. It assumes it would take seven days to make the seven layers. The cause of the appearance from the water is differential erosion between the flows causing them to stand out in relief. Spectacular gas-charged tubes called pipe vesicles are also common near the base of some of the flows and were probably caused by boiling of wet minerals under the flow. The pipes are generally the size of your hand and are filled with minerals. The formation flows dip about 10 to 12 degrees to the south-southeast so as you walk along the beach you will be travelling up through time.

At the posting coordinates you will find yourself looking up at the Seven Days Work formation and all of its layers. You are near one of the flows where you can examine the flow from top to bottom. Remember this is an earthcache so there is no container just an earth science lesson at an amazing natural feature that needs to be protected. To log this cache, email me through my profile:

1) The name of the Earthcache and the number of people in your group.

2) What is the thickness of the bottom layer and how does it compare in size and color to the layers that have formed above?

The access this location, follow the Whistle Road for about 1.5 km where you will find a place just past the old dump. If you go past this location you will cross Eel Brook and find another trail. Just head north down a well-worn path to Eel Brook Beach. Do not try to take a shorter path because you will only run into cliffs. This earthcache is best done at low tide.

If you would like more information on the geology of the area, Greg McHone has an outstanding webpage called Grand Manan Geology at (visit link)

Additional Hints (No hints available.)



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