This cache is to illustrate the contact between two rock types. If you consider that there are hundreds of rocks in this world, they must touch in lots of places. Contact between rock types is very common, and this is an easily accessible example of a contact.
The rock outcropping on the Stanley Park seawall is comprised of mainly two types of rock, sandstone a grey rock and basalt, a darker rock.
Basalt is called a hard rock and sandstone is called a soft rock.
Sandstone (sometimes known as arenite) is a clastic sedimentary rock composed mainly of sand-sized minerals or rock grains. It is a soft rock around the seawall.
Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow, red, grey, pink, white and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colours of sandstone have been strongly identified with certain regions.
Basalt is sometimes grey in colour, but rapidly weathers to brown or rust-red due to oxidation of its (iron-rich) minerals into rust. Basalt almost always has a fine-grained mineral texture due to the molten rock cooling too quickly for large mineral crystals to grow.
In this location on the seawall, the volcanic basalt has intruded the sandstone (part of the Tertiary Kitsilano formation), and is therefore younger than the sandstone. Most of Vancouver is underlain by sedimentary rocks, sandstone being the main one although there are other types of sedimentary rocks in other locations such as siltstone, conglomerate and shale.
The basalt has intruded the sandstone in the form of dykes. Dykes are commonly small and often culminate in volcanoes. Little mountain and Queen Elizabeth Park is such an example. Prospect point is an intrusive volcanic dyke, but it is commonly not thought to have culminated in a volcano (but the jury is still out on that one).
Sandstone is softer than basalt. The surfaces look different as the ice has smoothed the sandstone as it is relatively soft. The basalt, being relatively harder, and finer jointed, is smoother than the sandstone.
For this cache, go to the co-ordinates. You can stand behind the small metal fence so you are out of the way of bikes. Look at the contact in front of you. There is a little cave at the bottom of the contact. To log this earthcache, you must e-mail me the answer to these questions: (If possible, please use the e-mail option rather than the messenger option). Send me the answers at the same time you log your find. If your answers are wrong, your log will be deleted.
1. Which rock is on the left (east side) and which rock is on the right (west side). You can determine this by rubbing your hand on the rocks. The sandstone is softer, rougher and feels more like sandpaper, the basalt harder and smoother.
2. Estimate the angle of the contact coming down the cliff face, and is it angling down to the left (east) or right (west) (the dip of the contact).
3. How far apart are the two rocks?