The Drook Formation of Brigus
Brigus is home to unique geological earth formations. Above Brigus and beyond the end of John Noel’s Road is an ATV trail that leads to First Pond. This area has two very high hills on either side of the valley. The rock formation in this area is referred to in geological terms as the Drook Formation, also known as the Conception Group. These rocks formed during the late Neoproterozoic era (a unit of geologic time from about 1 billion to 541 million years ago). The rocks of the Drook Formation are made up of green siliceous siltstone and sandstone and silicified tuff. (Tuff is a type of rock consisting of consolidated volcanic ash).
Standing at the published coordinates you will find a good example of the siltstone and sandstone that makes up the Drook Formation. The small outcrop measuring some 20 feet in length and about 3 feet in height can be closely examined. Note the thin layering and rippling of the rock at this location. The layers have been compressed and thrusted upward to an angle of about 60 degrees. These rocks were formed more than 500 million years ago.
Standing in the same location, look east across the valley to see the massive outcrop of siltstone and sandstone that has been thrusted skyward more than 350 feet above sea level. You can easily appreciate the vertical layering of these rocks, in a North to South direction for almost a kilometer of exposed rock surface. Of note, is the cream color sheen that is seen over a very large portion of the rock surface. This color is produced by the weathering of the finely laminated siltstone and mudstone where it is directly exposed to the changing atmospheric conditions.
To claim this earthcache as a find please log the find and separately email me the answers to the following questions:
- What would be your estimate of the thickness of the very thin top, front most layer of the rock at the published coordinates?
- A small brook can be heard near by, and runs on which side (east or west) of the coordinates?
- During which geological time was the Drook Formation formed?
- What is the predominant color of the rock, other than the cream color?